126-501: The Ood are an alien species with telepathic abilities from the long-running science fiction series Doctor Who . In the series' narrative, they live in the distant future (circa 42nd century). The Ood are portrayed as a slave race, naturally gentle and kind but readily susceptible to corrupting external influence. They are later emancipated from their slavery and by " The End of Time " have progressed into an advanced civilization. The Ood are humanoid in appearance with tentacles on
252-510: A wedding dress , outraged to be inexplicably aboard the Doctor's TARDIS . The scene was kept a secret until broadcast, filmed with minimal crew, and was a humorous postscript to the sad farewell the Doctor shared with companion Rose ( Billie Piper ) moments prior. Donna's story is picked up in 2006 Christmas special " The Runaway Bride ". Donna is a temporary secretary at HC Clements in London,
378-416: A basic component of the development of a potential extraterrestrial technological civilization, as it is on Earth. Fossil fuels may likely be generated and used on such worlds as well. The abundance of chlorofluorocarbons in the atmosphere can also be a clear technosignature, considering their role in ozone depletion . Light pollution may be another technosignature, as multiple lights on the night side of
504-611: A catalog of microorganisms, with the way each one reacts to sunlight. The goal is to help with the search for similar organisms in exoplanets, as the starlight reflected by planets rich in such organisms would have a specific spectrum, unlike that of starlight reflected from lifeless planets. If Earth was studied from afar with this system, it would reveal a shade of green, as a result of the abundance of plants with photosynthesis. In August 2011, NASA studied meteorites found on Antarctica, finding adenine , guanine , hypoxanthine and xanthine . Adenine and guanine are components of DNA, and
630-507: A clone of the Doctor's nemesis the Master ( John Simm ), Donna's memories are nearly restored; however, a fail-safe installed by the Doctor protects her, as Donna generates a brief telepathic pulse that knocks out herself and the Masters in the vicinity. In the story's concluding moments, Donna is last seen when she marries new fiancé Shaun Temple ( Karl Collins ), becoming Donna Temple-Noble;
756-669: A fifth full book, called In the Blood , again with the Tenth Doctor, written by Jenny Colgan . Donna appears in Big Finish Productions ' fiftieth anniversary mini-series Destiny of the Doctor , appearing in the tenth story, Death's Deal , released in October 2013, with Tate returning to play the role. The series was co-produced with AudioGO , who at the time held the license to produce audio productions based on
882-804: A fourth and final appearance in the novels in Beautiful Chaos by Gary Russell in December 2008; subsequent Tenth Doctor novels in the New Series Adventures range feature the Doctor traveling alone. Donna also features in a number of Doctor Who short stories, in Doctor Who Annual 2009, and in The Doctor Who Storybook in 2007 and 2009, as well as making one online short story appearance "The Lonely Computer" (the events of which are briefly alluded to in
1008-481: A living entity must have the capacity to replicate itself, the capacity to avoid damage/decay, and the capacity to acquire and process resources in support of the first two capacities. Life on Earth started with an RNA world and later evolved to its current form, where some of the RNA tasks were transferred to DNA and proteins . Extraterrestrial life may still be stuck using RNA, or evolve into other configurations. It
1134-446: A major cultural impact, especially extraterrestrials in fiction . Science fiction has communicated scientific ideas, imagined a range of possibilities, and influenced public interest in and perspectives on extraterrestrial life. One shared space is the debate over the wisdom of attempting communication with extraterrestrial intelligence. Some encourage aggressive methods to try to contact intelligent extraterrestrial life. Others – citing
1260-534: A math equation, none of its values were known at the time. Although some values may eventually be measured, others are based on social sciences and are not knowable by their very nature. This does not allow one to make noteworthy conclusions from the equation. Based on observations from the Hubble Space Telescope , there are nearly 2 trillion galaxies in the observable universe. It is estimated that at least ten per cent of all Sun-like stars have
1386-472: A mixed aromatic - aliphatic structure") that could be created naturally, and rapidly, by stars . It is still unclear if those compounds played a role in the creation of life on Earth, but Sun Kwok, of the University of Hong Kong, thinks so. "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life." In August 2012, and in
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#17327726824951512-650: A planetary system formed by a star at the center, the Sun , and the objects that orbit it: other planets, moons, asteroids, and comets. The sun is part of the Milky Way , a galaxy . The Milky Way is part of the Local Group , a galaxy group that is in turn part of the Laniakea Supercluster . The universe is composed of all similar structures in existence. The immense distances between celestial objects
1638-466: A potential explanation to the Fermi paradox. If extraterrestrial life exists, it could range from simple microorganisms and multicellular organisms similar to animals or plants, to complex alien intelligences akin to humans . When scientists talk about extraterrestrial life, they consider all those types. Although it is possible that extraterrestrial life may have other configurations, scientists use
1764-570: A reasonable scientific explanation for any gathered data. In 1961, astronomer and astrophysicist Frank Drake devised the Drake equation as a way to stimulate scientific dialogue at a meeting on the search for extraterrestrial intelligence (SETI). The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilisations in the Milky Way galaxy . The Drake equation is: where: and Drake's proposed estimates are as follows, but numbers on
1890-443: A result has been conceived, even if hypothetical. Evolution requires life to be divided into individual organisms, and no alternative organisation has been satisfactorily proposed either. At the basic level, membranes define the limit of a cell, between it and its environment, while remaining partially open to exchange energy and resources with it. The evolution from simple cells to eukaryotes, and from them to multicellular lifeforms,
2016-399: A rocky planet can be a sign of advanced technological development. However, modern telescopes are not strong enough to study exoplanets with the required level of detail to perceive it. Donna Noble Donna Noble is a fictional character in the long-running British science fiction television series Doctor Who . Portrayed by British actress and comedian Catherine Tate , she
2142-468: A scale. Life on Earth is quite ubiquitous across the planet and has adapted over time to almost all the available environments in it, extremophiles and the deep biosphere thrive at even the most hostile ones. As a result, it is inferred that life in other celestial bodies may be equally adaptive. However, the origin of life is unrelated to its ease of adaptation, and may have stricter requirements. A celestial body may not have any life on it, even if it
2268-458: A security firm which, unbeknownst to her, is a front organization for the alien-investigating Torchwood Institute . Her parents are Geoff (Howard Attfield) and Sylvia Noble ( Jacqueline King ). Donna discovers that she is a pawn in a scheme of the Empress ( Sarah Parish ) of the alien Racnoss , having been manipulated by her fiancé , Lance ( Don Gilet ). When the Doctor unleashes his fury upon
2394-476: A series of factors that range from the location in the galaxy and the configuration of the Solar System to local characteristics of the planet, and that it is unlikely that all such requirements are simultaneously met by another planet. The proponents of this hypothesis consider that very little evidence suggests the existence of extraterrestrial life, and that at this point it is just a desired result and not
2520-579: A solvent other than water. The low temperatures required would add an extra problem, the difficulty to kickstart a process of abiogenesis to create life in the first place. Norman Horowitz , head of the Jet Propulsion Laboratory bioscience section for the Mariner and Viking missions from 1965 to 1976 considered that the great versatility of the carbon atom makes it the element most likely to provide solutions, even exotic solutions, to
2646-440: A star's light and heat, and so its lifeforms would not grow beyond a certain complexity. There is also research in assessing the capacity of life for developing intelligence. It has been suggested that this capacity arises with the number of potential niches a planet contains, and that the complexity of life itself is reflected in the information density of planetary environments, which in turn can be computed from its niches. It
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#17327726824952772-574: A story featuring the Judoon . Donna also appears in three original audiobooks published by BBC Books: Pest Control (May 2008), The Forever Trap (October 2008) and The Nemonite Invasion (February 2009). As indicated by David Tennant in his series two video diary (included in the DVD box set), the casting of Catherine Tate was kept secret; her scene in "Doomsday" was filmed with minimal crew. His series three video diary mentions that this instance
2898-665: A stronger telepathic force. Oods are a part of the Silence 's religious order. They also know the Doctor's name as they had sung it to him in "Planet of the Ood". The Ood have purple blood. The Ood debut in the Series 2 episode " The Impossible Planet ". They are used by humans as a slave race, performing all manner of menial tasks for the humans in the episode. They are described as offering themselves for servitude willingly, having no goals of their own except to be given orders and to serve. It
3024-660: A system of planets, i.e. there are 6.25 × 10 stars with planets orbiting them in the observable universe. Even if it is assumed that only one out of a billion of these stars has planets supporting life, there would be some 6.25 billion life-supporting planetary systems in the observable universe. A 2013 study based on results from the Kepler spacecraft estimated that the Milky Way contains at least as many planets as it does stars, resulting in 100–400 billion exoplanets. The apparent contradiction between high estimates of
3150-461: A world first, astronomers at Copenhagen University reported the detection of a specific sugar molecule, glycolaldehyde , in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422 , which is located 400 light years from Earth. Glycolaldehyde is needed to form ribonucleic acid , or RNA, which is similar in function to DNA. This finding suggests that complex organic molecules may form in stellar systems prior to
3276-402: Is life that originates from another world rather than on Earth . No extraterrestrial life has yet been scientifically conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent beings , possibly bringing forth civilizations that might be far more advanced than humans. The Drake equation speculates about the existence of sapient life elsewhere in
3402-512: Is a companion of the Tenth and Fourteenth Doctors (both portrayed by David Tennant ). Originally appearing in the closing scene of the show's 2006 series and as a special guest star in its following Christmas special, " The Runaway Bride ", Tate was not expected to reprise her role as Donna; for series 3 (2007) , the Doctor travelled alongside medical student Martha Jones ( Freema Agyeman ). However, Tate expressed interest in returning to
3528-537: Is a consequence of time "bleeding", and the elders of the Ood show the Doctor the dreams and prophesies they have been seeing. At the end of part two, Ood Sigma appears again to the Doctor and gives him the encouragement to return to his TARDIS to complete his regeneration into the Eleventh Doctor . "The End of Time" also introduces an Ood Elder, who has an exposed brain, crescent-shaped ears and yellowish tentacles. A single Ood referred to as Nephew appeared in
3654-601: Is a difficulty for the study of extraterrestrial life. So far, humans have only set foot on the Moon and sent robotic probes to other planets and moons in the Solar System. Although probes can withstand conditions that may be lethal to humans, the distances cause time delays: the New Horizons took nine years after launch to reach Pluto . No probe has ever reached extrasolar planetary systems. The Voyager 2 has left
3780-650: Is also claimed that they cannot look after themselves and that, if they do not receive orders, they pine away and die. The episode also alludes to a protest group called "Friends of the Ood" who oppose Ood slavery and seek to have them freed. According to the Official Doctor Who Annual 2007 , the Ood live on a planet in the Horsehead Nebula , where they were governed by a Hive Mind that was destroyed by human colonists. The BBC-authorised book Doctor Who: Creatures and Demons elaborates that
3906-501: Is also conceivable that there are forms of life whose solvent is a liquid hydrocarbon , such as methane , ethane or propane . Another unknown aspect of potential extraterrestrial life would be the chemical elements that would compose it. Life on Earth is largely composed of carbon, but there could be other hypothetical types of biochemistry . A replacement for carbon would need to be able to create complex molecules, store information required for evolution, and be freely available in
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4032-416: Is being carried out both directly and indirectly. As of September 2017 , 3,667 exoplanets in 2,747 systems have been identified , and other planets and moons in the Solar System hold the potential for hosting primitive life such as microorganisms . As of 8 February 2021, an updated status of studies considering the possible detection of lifeforms on Venus (via phosphine ) and Mars (via methane )
4158-403: Is common knowledge that the conditions on other planets in the solar system, in addition to the many galaxies outside of the Milky Way galaxy , are very harsh and seem to be too extreme to harbor any life. The environmental conditions on these planets can have intense UV radiation paired with extreme temperatures, lack of water, and much more that can lead to conditions that don't seem to favor
4284-485: Is complex and defined by several factors. Being in the habitable zone is not enough for a planet to be habitable, not even to actually have such liquid water. Venus is located in the habitable zone of the Solar System but does not have liquid water because of the conditions of its atmosphere. Jovian planets or gas giants are not considered habitable even if they orbit close enough to their stars as hot Jupiters , due to crushing atmospheric pressures. The actual distances for
4410-520: Is embodied in the Copernican principle , which states that Earth does not occupy a unique position in the Universe, and the mediocrity principle , which states that there is nothing special about life on Earth. Other authors consider instead that life in the cosmos, or at least multicellular life, may be actually rare. The Rare Earth hypothesis maintains that life on Earth is possible because of
4536-439: Is likely devoid of life. However, Venus is still of interest to astrobiologists, as it is a terrestrial planet that was likely similar to Earth in its early stages and developed in a different way. There is a greenhouse effect , the surface is the hottest in the Solar System, sulfuric acid clouds, all surface liquid water is lost, and it has a thick carbon-dioxide atmosphere with huge pressure. Comparing both helps to understand
4662-444: Is no guarantee that it is transmitting radio communications in the direction of Earth. The length of time required for a signal to travel across space means that a potential answer may arrive decades or centuries after the initial message. The atmosphere of Earth is rich in nitrogen dioxide as a result of air pollution , which can be detectable. The natural abundance of carbon, which is also relatively reactive, makes it likely to be
4788-657: Is not guaranteed. The Cambrian explosion took place thousands of millions of years after the origin of life, and its causes are not fully known yet. On the other hand, the jump to multicellularity took place several times, which suggests that it could be a case of convergent evolution , and so likely to take place on other planets as well. Palaeontologist Simon Conway Morris considers that convergent evolution would lead to kingdoms similar to our plants and animals, and that many features are likely to develop in alien animals as well, such as bilateral symmetry , limbs , digestive systems and heads with sensory organs . Scientists from
4914-464: Is revealed that the metacrisis had continued to subconsciously influence Donna and Rose, resulting in Donna giving away most of her lottery winnings to charity, as well as Rose choosing to name herself after Rose Tyler and making dolls inspired by the creatures that her mother had encountered with the Doctor. Donna and Rose safely expel the metacrisis, and Donna accepts the Doctor's offer of one last trip in
5040-466: Is that the chemical elements that make up life, such as carbon and water, are ubiquitous in the universe. The third is that the physical laws are universal, which means that the forces that would facilitate or prevent the existence of life would be the same ones as on Earth. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking , it would be improbable for life not to exist somewhere else other than Earth. This argument
5166-421: Is that there are natural sources of such signals as well, such as gamma-ray bursts and supernovae, and the difference between a natural signal and an artificial one would be in its specific patterns. Astronomers intend to use artificial intelligence for this, as it can manage large amounts of data and is devoid of biases and preconceptions. Besides, even if there is an advanced extraterrestrial civilization, there
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5292-447: Is unclear if our biochemistry is the most efficient one that could be generated, or which elements would follow a similar pattern. However, it is likely that, even if cells had a different composition to those from Earth, they would still have a cell membrane . Life on Earth jumped from prokaryotes to eukaryotes and from unicellular organisms to multicellular organisms through evolution . So far no alternative process to achieve such
5418-778: The Rio Tinto river in Spain. NASA officials soon distanced NASA from the scientists' claims, and Stoker herself backed off from her initial assertions. In November 2011, NASA launched the Mars Science Laboratory that landed the Curiosity rover on Mars. It is designed to assess the past and present habitability on Mars using a variety of scientific instruments. The rover landed on Mars at Gale Crater in August 2012. A group of scientists at Cornell University started
5544-459: The hydrothermal vents found on the ocean floor are known to support many chemosynthetic processes which allow organisms to utilize energy through reduced chemical compounds that fix carbon. In return, these reactions will allow for organisms to live in relatively low oxygenated environments while maintaining enough energy to support themselves. The early Earth environment was reducing and therefore, these carbon fixing compounds were necessary for
5670-485: The 15th century, acknowledged the possibility Jesus could have visited extraterrestrial worlds to redeem their inhabitants. Nicholas of Cusa wrote in 1440 that Earth is "a brilliant star" like other celestial objects visible in space; which would appear similar to the Sun , from an exterior perspective, due to a layer of "fiery brightness" in the outer layer of the atmosphere. He theorised all extraterrestrial bodies could be inhabited by men, plants, and animals, including
5796-471: The 2008 series, he is introduced properly as Donna's grandfather, following the death of actor Howard Attfield. In the series four opener " Partners in Crime " (2008), two years later, Donna has become dissatisfied with regular life and more interested in the bigger picture after her father died. When both are investigating the alien connection to Adipose Industries ' Miss Foster ( Sarah Lancashire ), she and
5922-618: The Doctor are re-united, and she joins him in the TARDIS as a regular companion. In " The Fires of Pompeii ", Donna shows her compassion when she argues and convinces the Doctor to save a family in Pompeii from the eruption of Mount Vesuvius . In " Planet of the Ood ", Donna and the Doctor go to the Ood-Sphere and Donna defends the Ood from the abuses they suffer at the hands of humans. In
6048-402: The Doctor's energised severed hand and is imbued with the totality of his knowledge, with which she is able to stop Davros ( Julian Bleach ) and his plan to destroy reality. However, because her mind cannot handle the knowledge, the Doctor is forced to wipe her memory of him against her wishes. He hopes that they never meet again, lest she remember and her mind "burn up". Donna reappears in
6174-526: The Doctor. The Ood also appear in the following episode, the two-part story " The End of Time ". In this episode, the Doctor finally accepts Ood Sigma's message and returns to the Ood Sphere 100 years (in their time line) after having freed them in "Planet of the Ood". The Doctor discovers that the Ood's civilisation has advanced too rapidly, and that the Ood have developed the ability to see and project themselves through time itself. The Ood reveal that this
6300-800: The Ood " that Ood individuality is a result of the Ood Hive Mind expressing itself differently within each Ood, saying "Funny thing, the subconscious. Takes all sorts of shapes. Came out in the Red-Eye as revenge, came out in the Rabid Ood as anger, and then there was patience. All that intelligence and mercy focused on Ood Sigma." The Ood are empaths , sharing among themselves a low-level telepathic communication field. When reaching out with their telepathic fields, it can be heard as singing. This ability has made them susceptible to telepathic control, and in several episodes they are shown to be controlled by
6426-539: The Ood came from the Ood Sphere. The Ood Sphere is close to the Sense Sphere planet, home to the Sensorites , who share a mental and physical similarity with the Ood. Without a hive mind, the Ood offered themselves to the human colonists and became a slave race. The Tenth Doctor and Rose Tyler encounter fifty Ood accompanying a human-led expeditionary force in "The Impossible Planet". The empathic nature of
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#17327726824956552-407: The Ood for 200 years by Ood Operations, the corporation that processed the Ood slaves; however, the Ood known as Sigma, who appears as the personal servant of Ood Operations leader Halpen, has been advancing the Ood freedom, by slowly turning him into an Ood and lowering the barrier around the giant brain that links all Ood together. The possessed "red eyed" Ood reappear in this episode, running amok at
6678-495: The Ood made them susceptible to psychic possession by the Beast , who formed the Ood on the base into his "Legion". While possessed, the Ood's eyes changed color to red and they killed several humans by throwing their translation spheres at them and electrocuting them. At the end of the episode, the Doctor was forced to sacrifice all the surviving Ood to the black hole around the planet because he did not have time to save both them and
6804-428: The Ood, though the Doctor seems to be able to determine their sex. When Donna refers to a dying Ood as an "it", the Doctor replies that the Ood is "a 'he', not an 'it'". The Ood say they require no names or titles as they are connected to a hive mind and function as one unit, but they do have designations given to them by humans such as "Ood 1 Alpha 1" or "Ood Sigma" to differentiate them. The Doctor suggests in " Planet of
6930-568: The Racnoss, Donna snaps him out of it and together they escape before the Torchwood facility floods. Donna is upset, having lost her job and her fiancé, and declines the Doctor's offer to become his companion, though she advises he find one. Donna does not appear in the 2007 series, but the character Wilfred Mott ( Bernard Cribbins ) appears in 2007 Christmas special " Voyage of the Damned "; in
7056-478: The Solar System at a speed of 50,000 kilometers per hour, if it headed towards the Alpha Centauri system, the closest one to Earth at 4.4 light years, it would reach it in 100,000 years. Under current technology such systems can only be studied by telescopes, which have limitations. It is estimated that dark matter has a larger amount of combined matter than stars and gas clouds, but as it plays no role on
7182-478: The Sun. Descartes wrote that there was no means to prove the stars were not inhabited by "intelligent creatures", but their existence was a matter of speculation. When considering the atmospheric composition and ecosystems hosted by extraterrestrial bodies, extraterrestrial life can seem more speculation than reality, due to the harsh conditions and disparate chemical composition of the atmospheres, when compared to
7308-586: The TARDIS to see Wilfred. However, Donna accidentally spills coffee on the TARDIS console, sending it flying out of control. Following the ensuing chaos, the TARDIS strands the Doctor and Donna on a spaceship on the edge of the known universe in " Wild Blue Yonder ". They are tormented by two shapeshifting creatures who impersonate them, and the Doctor almost leaves Donna to die aboard the exploding spacecraft after mistaking her for her doppelgänger. He realises his mistake and rescues Donna just in time. They return to London where they are reunited with Wilf, who informs them
7434-414: The Tenth Doctor's prior companions, who both harboured romantic feelings for him, Donna and the Doctor shared a strictly platonic relationship ; and she did not feel the need to prove herself to be allowed to travel with the Doctor, who refers to her as his "best friend". Donna Noble makes her first appearance, credited as "The Bride", in the closing scenes of 2006 series finale " Doomsday "; she appears in
7560-625: The University of Oxford analysed it from the perspective of evolutionary theory and wrote in a study in the International Journal of Astrobiology that aliens may be similar to humans. The planetary context would also have an influence: a planet with higher gravity would have smaller animals, and other types of stars can lead to non-green photosynthesizers . The amount of energy available would also affect biodiversity , as an ecosystem sustained by black smokers or hydrothermal vents would have less energy available than those sustained by
7686-665: The Wasp " and have to solve their very own murder mystery with Agatha Christie and a giant alien wasp. The two-parter episodes of " Silence in the Library " and " Forest of the Dead " introduces River Song ( Alex Kingston ) and the Doctor accidentally shoves Donna into a cyberworld while attempting to keep her safe from the Vashta Nerada . She then falls in love with Lee McAvoy and has two children with him. However, she discovers that
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#17327726824957812-410: The area surrounding these hydrothermal vents which can suggest that some form of life can be supported even in the harshest of environments like the other planets in the solar system. The aspects of these harsh environments that make them ideal for the origin of life on Earth, as well as the possibility of creation of life on other planets, is the chemical reactions forming spontaneously. For example,
7938-568: The atom speeds, either too fast or too slow, make it difficult for specific ones to meet and start chemical reactions. A liquid medium also allows the transport of nutrients and substances required for metabolism. Sufficient quantities of carbon and other elements, along with water, might enable the formation of living organisms on terrestrial planets with a chemical make-up and temperature range similar to that of Earth. Life based on ammonia rather than water has been suggested as an alternative, though this solvent appears less suitable than water. It
8064-400: The behest of the hive mind. After being freed, all Ood across the universe are returned to the Ood Sphere. While there, Ood Sigma refers to Donna Noble as "Doctor-Donna" and prophesizes that the Doctor's "song" will soon come to an end. Ood Sigma returns as part of the 2008–10 specials in the episode " The Waters of Mars ", where he appears at the end of the episode in an attempt to contact
8190-518: The character was not originally scheduled to return at all. Donna did not appear in his original conception of reunion episode "The Stolen Earth", despite planned reappearances from Martha, Captain Jack (Barrowman), Sarah Jane (Sladen), Rose (Piper), Jackie Tyler ( Camille Coduri ), as well as Mickey Smith ( Noel Clarke ), Elton Pope from series 2 episode " Love & Monsters ", and the cast of spin-off series Torchwood . Davies originally intended
8316-481: The character's comedic scenes in Digital Spy . In their review of the fourth series, Digital Spy opined "At the core was Catherine Tate's excellent performance as Donna Noble, epitomising the intricate fusion of fun, adventure, sadness and a desire to belong." Digital Spy noted that fans initially worried about Tate's full-time casting, as she is known for her role as a comedian and comic actor. They attributed
8442-403: The character's success to the modification of the much more brash and boisterous character she appeared to be in "The Runaway Bride". The character's comedic elements continued ("the occasional... misfire") in the form of her tendency to shout, but Digital Spy was praising of many of the character's comedic moments. They praised more highly Tate's crying scenes in "The Fires of Pompeii", which "gave
8568-402: The cold temperatures would make such chemistry take place at a very slow pace. Water is rock-solid on the surface, but Titan does have a subsurface water ocean like several other moons. However, it is of such a great depth that it would be very difficult to access it for study. The science that searches and studies life in the universe, both on Earth and elsewhere, is called astrobiology . With
8694-521: The creation or maintenance of extraterrestrial life. However, there has been much historical evidence that some of the earliest and most basic forms of life on Earth originated in some extreme environments that seem unlikely to have harbored life at least at one point in Earth's history. Fossil evidence as well as many historical theories backed up by years of research and studies have marked environments like hydrothermal vents or acidic hot springs as some of
8820-444: The difficulty for life to appear was not the temperature, but the scarcity of free heavy elements. Planetary systems emerged, and the first organic compounds may have formed in the protoplanetary disk of dust grains that would eventually create rocky planets like Earth. Although Earth was in a molten state after its birth and may have burned any organics that fell in it, it would have been more receptive once it cooled down. Once
8946-449: The dying Doctor anonymously delivers her a winning lottery ticket to ensure her financial future, having borrowed the purchase price from Donna's late father in the past, making it a present from both him and the Doctor. In " The Star Beast " (2023), Donna is reunited with the recently-regenerated Fourteenth Doctor , who has the face of the Tenth Doctor. Donna and Shaun now have a transgender daughter named Rose, who comes into contact with
9072-568: The end for the scene despite it being cut. In the Pond Life series, a single Ood who had become lost in the TARDIS wanders out into Amy and Rory 's house. The Ood acts as their butler for several days until the Doctor can pick it up and return it to the Ood Sphere. An Ood appears in Survivors of the Flux , serving as Tecteun's assistant who is powering the next wave of the Flux to destroy
9198-413: The end, the star blows much of its content back into the stellar medium, where it would join clouds that would eventually become new generations of stars and planets. Many of those materials are the raw components of life on Earth. As this process takes place in all the universe, said materials are ubiquitous in the cosmos and not a rarity from the Solar System. Earth is a planet in the Solar System ,
9324-617: The episode " The Unicorn and the Wasp "). The character also features prominently in comic books and comic strips featured in Doctor Who Magazine , the younger-audience Doctor Who Adventures , and Doctor Who: Battles in Time , online comic book features, comics featured in the Annual , and Storybook , as well as in two arcs of American comic book company IDW Publishing 's Doctor Who ongoing series. In 2016, she would star in
9450-656: The events. In "The Giggle," Kate Stewart, impressed with Donna's skills, had offered her a job. Outside of the television series, Donna appears in some of the BBC Books New Series Adventures novels, alongside the Tenth Doctor, in stories set in-between episodes of series four. Donna first appears in Ghosts of India by Mark Morris , The Doctor Trap by Simon Messingham, and Shining Darkness by Mark Michalowski in September 2008. She makes
9576-403: The first hominids appeared 60 million years ago. Life on other planets may have started, evolved, given birth to extraterrestrial intelligences, and perhaps even faced a planetary extinction event millions or even billions of years ago. The brief times of existence of Earth's species, when considered from a cosmic perspective, may suggest that extraterrestrial life may be equally fleeting under such
9702-466: The first places that life could have originated on Earth. These environments can be considered extreme when compared to the typical ecosystems that the majority of life on Earth now inhabit, as hydrothermal vents are scorching hot due to the magma escaping from the Earth's mantle and meeting the much colder oceanic water. Even in today's world, there can be a diverse population of bacteria found inhabiting
9828-410: The formation of planets, eventually arriving on young planets early in their formation. In December 2023, astronomers reported the first time discovery, in the plumes of Enceladus , moon of the planet Saturn , of hydrogen cyanide , a possible chemical essential for life as we know it, as well as other organic molecules , some of which are yet to be better identified and understood. According to
9954-455: The giant planets themselves are highly unlikely to have life, there is much hope to find it on moons orbiting these planets. Europa , from the Jovian system, has a subsurface ocean below a thick layer of ice. Ganymede and Callisto also have subsurface oceans, but life is less likely in them because water is sandwiched between layers of solid ice. Europa would have contact between the ocean and
10080-404: The habitable zones vary according to the type of star, and even the solar activity of each specific star influences the local habitability. The type of star also defines the time the habitable zone will exist, as its presence and limits will change along with the stars stellar evolution. The Big Bang took place 14 billion years ago, the Solar System was formed 4 and a half billion years ago, and
10206-571: The hierarchy of lifeforms from Earth for simplicity, as it is the only one known to exist. The first basic requirement for life is an environment with non-equilibrium thermodynamics , which means that the thermodynamic equilibrium must be broken by a source of energy. The traditional sources of energy in the cosmos are the stars, such as for life on Earth, which depends on the energy of the sun. However, there are other alternative energy sources, such as volcanoes , plate tectonics , and hydrothermal vents . There are ecosystems on Earth in deep areas of
10332-436: The human crew. The Ood return in the Series 4 episode " Planet of the Ood ", where it is revealed that they are not born to serve but are an enslaved race. The Ood translation spheres actually replaced their hind brain which had contained their individual personalities. The Doctor successfully frees the Ood by releasing the Ood hive mind, which connects all the Ood with a telepathic link. The hive mind had been sequestered from
10458-477: The intergalactic criminal Beep the Meep . The Doctor is forced to team up with Donna again, although he desperately attempts to keep his old friend from remembering. With all of London in danger, the Doctor is forced to restore Donna's memories and the "DoctorDonna" in order to stop the Meep. However, Rose has partially inherited the metacrisis from Donna, stabilizing her enough to survive her memories being returned. It
10584-440: The life-abundant Earth. However, there are many extreme and chemically harsh ecosystems on Earth that do support forms of life and are often hypothesized to be the origin of life on Earth. Hydrothermal vents , acidic hot springs, and volcanic lakes are examples of life forming under difficult circumstances, provide parallels to the extreme environments on other planets and support the possibility of extraterrestrial life. Since
10710-438: The lower portions of their faces. The Ood are a telepathic race; as such, they require a "translation sphere" to communicate with non-telepathic creatures. The sphere is connected to the Ood via a tube that originally connected their external brains to their body. Humans in the future would physically remove their hind brains and fix the translator sphere where the brain used to be. There appears to be no sexual differentiation among
10836-543: The medium. To create DNA , RNA , or a close analog, such an element should be able to bind its atoms with many others, creating complex and stable molecules. It should be able to create at least three covalent bonds: two for making long strings and at least a third to add new links and allow for diverse information. Only nine elements meet this requirement: boron , nitrogen , phosphorus , arsenic , antimony (three bonds), carbon , silicon , germanium and tin (four bonds). As for abundance, carbon, nitrogen, and silicon are
10962-478: The mid-20th century, active research has taken place to look for signs of extraterrestrial life, encompassing searches for current and historic extraterrestrial life, and a narrower search for extraterrestrial intelligent life . Depending on the category of search, methods range from analysis of telescope and specimen data to radios used to detect and transmit communications. The concept of extraterrestrial life, and particularly extraterrestrial intelligence, has had
11088-463: The mini episode " Death is the Only Answer ", the scientist Albert Einstein is transformed into a red-eyed Ood after ingesting a mysterious liquid. The possessed Ood repeats the phrase "Death is the only answer" before being transformed back into Einstein. A scene cut from " A Good Man Goes to War " would have seen the Doctor meeting up with Ood Sigma again. Russell T Davies is still credited at
11214-572: The most abundant ones in the universe, far more than the others. On Earth's crust the most abundant of those elements is silicon, in the Hydrosphere it is carbon and in the atmosphere, it is carbon and nitrogen. Silicon, however, has disadvantages over carbon. The molecules formed with silicon atoms are less stable, and more vulnerable to acids, oxygen, and light. An ecosystem of silicon-based lifeforms would require very low temperatures, high atmospheric pressure , an atmosphere devoid of oxygen, and
11340-504: The native planet that may not be caused by natural causes. There are three main types of techno-signatures considered: interstellar communications , effects on the atmosphere, and planetary-sized structures such as Dyson spheres . Organizations such as the SETI Institute search the cosmos for potential forms of communication. They started with radio waves , and now search for laser pulses as well. The challenge for this search
11466-555: The next opportunity arises. Donna becomes an asset to the Doctor on his adventures and on being merged with Time Lord energy, becomes the DoctorDonna and ultimately saves the universe, albeit at the cost of the memories of her travels with the Doctor. Donna's memories are restored years later, when the Doctor returns as a new incarnation with a similar appearance , and the Doctor ultimately settles down with her and her family after bi-generating another incarnation . In contrast to
11592-418: The ocean that do not receive sunlight, and take energy from black smokers instead. Magnetic fields and radioactivity have also been proposed as sources of energy, although they would be less efficient ones. Life on Earth requires water in a liquid state as a solvent in which biochemical reactions take place. It is highly unlikely that an abiogenesis process can start within a gaseous or solid medium:
11718-568: The origin of extraterrestrial life. The Solar System has a wide variety of planets, dwarf planets, and moons, and each one is studied for its potential to host life. Each one has its own specific conditions that may benefit or harm life. So far, the only lifeforms found are those from Earth. No extraterrestrial intelligence other than humans exists or has ever existed within the Solar System. Astrobiologist Mary Voytek points out that it would be unlikely to find large ecosystems, as they would have already been detected by now. The inner Solar System
11844-468: The others are used in other biological processes. The studies ruled out pollution of the meteorites on Earth, as those components would not be freely available the way they were found in the samples. This discovery suggests that several organic molecules that serve as building blocks of life may be generated within asteroids and comets. In October 2011, scientists reported that cosmic dust contains complex organic compounds ("amorphous organic solids with
11970-553: The planetary core ceased to generate a magnetic field, solar winds removed the atmosphere and the planet became vulnerable to solar radiation. Ancient life-forms may still have left fossilised remains, and microbes may still survive deep underground. As mentioned, the gas giants and ice giants are unlikely to contain life. The most distant solar system bodies, found in the Kuiper Belt and outwards, are locked in permanent deep-freeze, but cannot be ruled out completely. Although
12096-511: The precise differences that lead to beneficial or harmful conditions for life. And despite the conditions against life on Venus , there are suspicions that microbial life-forms may still survive in high-altitude clouds. Mars is a cold and almost airless desert, inhospitable to life. However, recent studies revealed that water on Mars used to be quite abundant, forming rivers, lakes, and perhaps even oceans. Mars may have been habitable back then, and life on Mars may have been possible. But when
12222-456: The probability of the existence of extraterrestrial civilisations and the lack of evidence for such civilisations is known as the Fermi paradox . Dennis W. Sciama claimed that life's existence in the universe depends on various fundamental constants. Zhi-Wei Wang and Samuel L. Braunstein suggest that a random universe capable of supporting life is likely to be just barely able to do so, giving
12348-476: The probe to study ocean water. Still, Cassini detected complex organic molecules, salts, evidence of hydrothermal activity, hydrogen, and methane. Titan is the only celestial body in the Solar System besides Earth that has liquid bodies on the surface. It has rivers, lakes, and rain of hydrocarbons, methane, and ethane, and even a cycle similar to Earth's water cycle . This special context encourages speculations about lifeforms with different biochemistry, but
12474-438: The problems of survival of life on other planets. However, he also considered that the conditions found on Mars were incompatible with carbon based life. Even if extraterrestrial life is based on carbon and uses water as a solvent, like Earth life, it may still have a radically different biochemistry . Life is generally considered to be a product of natural selection . It has been proposed that to undergo natural selection
12600-465: The remaining universe. After Tecteun is killed by Swarm and Azure, he assists the Doctor in trying to alter the course of the Flux wave. The Ood were physically portrayed by actor Paul Kasey . The Ood Elder in The End of Time is voiced by Brian Cox , whilst all other Ood are voiced by Silas Carson . Extraterrestrial life Extraterrestrial life , or alien life (colloquially, alien ),
12726-433: The researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life ." Although most searches are focused on the biology of extraterrestrial life, an extraterrestrial intelligence capable enough to develop a civilization may be detectable by other means as well. Technology may generate technosignatures , effects on
12852-804: The revived series. Following the folding of AudioGO and Big Finish's acquisition of the new series license, Tate reprises the role once again in Doctor Who: The Tenth Doctor Adventures in May 2016, with David Tennant reprising the Tenth Doctor. The stories include Technophobia , Time Reaver and Death and the Queen . In 2019, Donna featured in the third volume of the Tenth Doctor Adventures alongside The Tenth Doctor ( David Tennant ), Wilfred Mott ( Bernard Cribbins ) and Sylvia Noble ( Jacqueline King ), with
12978-426: The right conditions on Earth were met, life started by a chemical process known as abiogenesis . Alternatively, life may have formed less frequently, then spread – by meteoroids , for example – between habitable planets in a process called panspermia . During most of its stellar evolution stars combine hydrogen nuclei to make helium nuclei by stellar fusion, and the comparatively lighter weight of helium allows
13104-405: The right side of the equation are agreed as speculative and open to substitution: 10,000 = 5 ⋅ 0.5 ⋅ 2 ⋅ 1 ⋅ 0.2 ⋅ 1 ⋅ 10,000 {\displaystyle 10{,}000=5\cdot 0.5\cdot 2\cdot 1\cdot 0.2\cdot 1\cdot 10{,}000} The Drake equation has proved controversial since, although it is written as
13230-422: The rocky surface, which helps the chemical reactions. It may be difficult to dig so deep in order to study those oceans, though. Enceladus , a tiny moon of Saturn with another subsurface ocean, may not need to be dug, as it releases water to space in eruption columns . The space probe Cassini flew inside one of these, but could not make a full study because NASA did not expect this phenomenon and did not equip
13356-533: The role, and returned as a series regular in series 4 (2008) , the subsequent 2009–2010 Christmas and New Year's special , and in the 60th anniversary specials in 2023. Within the series' narrative, Donna begins as an outspoken Londoner in her mid-30s, a temp worker from Chiswick whose view of the universe is small in scope. Although she at first finds alien time traveller the Doctor terrifying, their initial encounter leaves her unsatisfied with her normal life and she decides to travel alongside him when
13482-532: The same samples suggests that a non-biological reaction is a more likely hypothesis. In February 2005 NASA scientists reported they may have found some evidence of extraterrestrial life on Mars. The two scientists, Carol Stoker and Larry Lemke of NASA's Ames Research Center , based their claim on methane signatures found in Mars's atmosphere resembling the methane production of some forms of primitive life on Earth, as well as on their own study of primitive life near
13608-525: The series four companion to be "Penny", a Northern woman with whom the Doctor would share a romantic attraction. After a conversation between Catherine Tate and the BBC's Jane Tranter , in which Tate expressed an interest in returning, Davies rewrote season four to bring Donna back as the new full-time companion instead. Tate looked to her own full-time casting as a "gamble" on the part of executive producer Russell T Davies; Tate attributes this to being "known, by
13734-431: The series six episode " The Doctor's Wife ". Nephew is under the influence of an alien entity called House. Nephew is killed when the Doctor and Idris land a TARDIS console in the exact spot he was standing, vaporising him instantly. The Doctor remarks that Nephew was "another Ood I failed to save", a reference to his previous encounters. Nephew's eyes glow green when possessed, a change from the red in previous episodes. In
13860-411: The sheer visual hilarity of her silent first encounter with The Doctor in 'Partners In Crime', or her attempts to blend in to the deliciously Cluedo-esque world in 'The Unicorn And The Wasp'? Then there was her paraphrased Alan Partridge homage in 'The Poison Sky', quipping "back of the neck!" after offing a Sontaran via its probic vent. Pure "wizard", as Donna would put it. Ben Rawson-Jones, praising
13986-399: The star to release the extra energy. The process continues until the star uses all of its available fuel, with the speed of consumption being related to the size of the star. During its last stages, stars start combining helium nuclei to form carbon nuclei. The higher-sized stars can further combine carbon nuclei to create oxygen and silicon, oxygen into neon and sulfur, and so on until iron. In
14112-482: The stellar evolution of stars and planets, it is usually not taken into account by astrobiology. There is an area around a star, the circumstellar habitable zone or "Goldilocks zone", where water may be at the right temperature to exist in liquid form at a planetary surface. This area is neither too close to the star, where water would become steam, nor too far away, where water would be frozen as ice. However, although useful as an approximation, planetary habitability
14238-508: The study of Earth's life, the only known form of life, astrobiology seeks to study how life starts and evolves and the requirements for its continuous existence. This helps to determine what to look for when searching for life in other celestial bodies. This is a complex area of study, and uses the combined perspectives of several scientific disciplines, such as astronomy , biology , chemistry , geology , oceanography , and atmospheric sciences . The scientific search for extraterrestrial life
14364-539: The survival and possible origin of life on Earth . With the little amount of information that scientists have found regarding the atmosphere on other planets in the Milky Way galaxy and beyond, the atmospheres are most likely reducing or with very low oxygen levels, especially when compared with Earth's atmosphere. If there were the necessary elements and ions on these planets, the same carbon fixing, reduced chemical compounds occurring around hydrothermal vents could also occur on these planets' surfaces and possibly result in
14490-636: The tendency of technologically advanced human societies to enslave or destroy less advanced societies – argue it may be dangerous to actively draw attention to Earth. Initially, after the Big Bang the universe was too hot to allow life. 15 million years later , it cooled to temperate levels, but the elements that make up living things did not exist yet. The only freely available elements at that point were hydrogen and helium . Carbon and oxygen (and later, water ) would not appear until 50 million years later, created through stellar fusion. At that point,
14616-675: The two Doctors defeat the Toymaker, Donna encourages the Fourteenth Doctor to remain on Earth with her and her family to recover from the trauma of his recent life. He accepts and moves in with the Noble-Temple family, later acknowledging to Donna that his time with them is the happiest he's ever been. In " The Legend of Ruby Sunday ", Rose helps UNIT with a case investigating S Triad Tech and mentions to Ruby that she and Donna work for UNIT now, although Donna isn't present during
14742-414: The two-part " The End of Time " (2009–2010). Early in the story, she buys her grandfather a book written by the episode's villain, which the Doctor takes to mean that the "DoctorDonna" is still trying to subconsciously lend a hand. When every member of the human race (apart from herself and Wilfred, attributed to Wilfred being shielded and Donna's DNA still being slightly altered after the meta-crisis) becomes
14868-544: The two-parter " The Sontaran Stratagem " and " The Poison Sky ", Donna meets the Doctor's former companion Martha Jones ( Freema Agyeman ) who works for UNIT and together they stop the Sontarans from using ATMOS to choke the world. In " The Doctor's Daughter ", it is Donna who names the eponymous character " Jenny " ( Georgia Tennant ) and subsequently convinces the Doctor to accept Jenny. The Doctor and Donna meet Agatha Christie ( Fenella Woolgar ) in " The Unicorn and
14994-608: The universe. The science of extraterrestrial life is known as astrobiology . Speculation about the possibility of inhabited worlds beyond Earth dates back to antiquity. Early Christian writers discussed the idea of a "plurality of worlds" as proposed by earlier thinkers such as Democritus ; Augustine references Epicurus 's idea of innumerable worlds "throughout the boundless immensity of space" in The City of God . Pre-modern writers typically assumed extraterrestrial "worlds" are inhabited by living beings. William Vorilong , in
15120-445: The unusual properties of the meteorite were eventually explained as the result of inorganic processes, the controversy over its discovery laid the groundwork for the development of astrobiology. An experiment on the two Viking Mars landers reported gas emissions from heated Martian soil samples that some scientists argue are consistent with the presence of living microorganisms. Lack of corroborating evidence from other experiments on
15246-520: The vast majority of people, for wearing wigs and comedy teeth" (in her sketch comedy The Catherine Tate Show ). The actress was grateful to Davies for casting her, and joked about the prominence eventually afforded her character: "For one brief moment I was the most important woman in the whole of the universe." Ben Rawson-Jones attributes success to the natural progression of her character, her boisterous personality being toned down for her first 2008 appearance, "Partners in Crime". Who can ever forget
15372-492: The world is in crisis once again and needs their help. Donna accompanies the Doctor to UNIT's headquarters in " The Giggle ", where she meets UNIT's new leader Kate Lethbridge-Stewart ( Jemma Redgrave ) and the Doctor's former companion Mel Bush ( Bonnie Langford ). They battle with the Toymaker ( Neil Patrick Harris ), an old nemesis of the Doctor, who forces him to bi-generate, creating his fifteenth incarnation ( Ncuti Gatwa ) in co-existence with his fourteenth self. After
15498-473: The world she is in and her children are actually digital replications, the revelation severely traumatising her. " Midnight " gives Donna a break with a spa day while the Doctor has the most terrifying bus ride of his life. The episode " Turn Left " features a parallel universe wherein Donna never met the Doctor; consequently, the Doctor died and the world comes to an end much sooner. In finale episodes " The Stolen Earth " and " Journey's End ", Donna touches
15624-417: Was habitable. It is unclear if life and intelligent life are ubiquitous in the cosmos or rare. The hypothesis of ubiquitous extraterrestrial life relies on three main ideas. The first one, the size of the universe allows for plenty of planets to have a similar habitability to Earth, and the age of the universe gives enough time for a long process analog to the history of Earth to happen there. The second
15750-599: Was one of the few occasions where the element of surprise was successfully maintained without it being revealed in advance by the media. Tate became the first guest star to be named in the show's opening credits, which has since become common practice in the show's specials. Her character was considered by the production team to have companion status long before the announcement of the character's return. Executive producer Russell T Davies at one time dismissed Donna's potential as an ongoing companion due to her abrasive personality, saying that "she'd get on your nerves". In fact,
15876-399: Was reported. Scientists search for biosignatures within the Solar System by studying planetary surfaces and examining meteorites . Some claim to have identified evidence that microbial life has existed on Mars. In 1996, a controversial report stated that structures resembling nanobacteria were discovered in a meteorite, ALH84001 , formed of rock ejected from Mars . Although all
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