The first space telescope to track the exoplanets is French. The industrial contract was signed June 19, 2003 between CNES and Alcatel. Corot is responsible for detecting extrasolar planets in other solar systems and explore the mysteries concealed in the heart of stars. The mission conducted under the auspices of the Center National d'Etudes Spatiales (CNES) is conducted in cooperation with international participation of the European Space Agency (ESA) and various countries mostly European. Convection and rotation refers to the ability of satellite to probe the interior of stars to study the acoustic waves that ripple across the surface, a technique called stellar seismology" asteroseismology.
Transit global refers to the technique used to detect the presence of a planet orbiting a star with the decrease in brightness caused it past the star. To fill its two scientific objectives, COROT will monitor some 120 000 stars with his telescope of 30 cm in diameter. The satellite is located at 900 km altitude in a circular orbit with an inclination of 90 °. This altitude can be repeated every seven days the cycle of operations. This orbit was chosen because it allows continuous observation for more than 150 days, the center of the galaxy, and was in the opposite direction in winter.
It is unlikely that the Space Telescope uncovers planets the size of Earth. During the 10 years that followed the discovery in 1995 of the first exoplanet, 51 Pegasi b, 220 planets have been detected by large ground-based observatories. The satellite COROT promises to find many more during its two-year mission and a half and push the limits of our knowledge allowing us to discover planets of smaller and smaller. When train its instruments on a star, COROT will also observe "stellar earthquakes, these acoustic waves generated deep inside a star that send ripples across its surface, altering its brightness. The nature of the ripples allows astronomers to calculate the precise mass, age and chemical composition of stars.
CoRoT has garnered a rich harvest in 2006 and unearthed in 2009, the smallest exoplanets. Unfortunately, this planet orbits very close to its star and hence its surface temperature reached 1 500 ° C.
NB: This is a 2.1B Soyuz rocket, which took off at 15h23 (Paris time) December 27, 2006 from its launch pad of the Baikonur Cosmodrome to file COROT in orbit.
The space Telescope Spitzer Lyman Spitzer, Jr. (In June 26th, 1914 - March 31st, 1997) was an American astrophysicist, an author about 200 scientific articles (according to ADS / CDS (Nasa)), among whom 155 in first author. According to his biography, he would be the first one to have expressed the idea to send an in orbit ground telescope. He participated actively in the realization of the project of the spatial telescope Hubble. He was a prize-winner of the Medal Franklin in 1980 for his research works on the mechanisms of formation of stars. His name was given to the spatial telescope Spitzer (SIRTF) when it was sent into orbit. Spitzer is the biggest infrared telescope launched by the NASA. These wavelengths which can not be usefully observed since the ground, only an object outside of the atmosphere, cooled cryogenically can make useful observations.
This satellite is similar to the spatial telescope ISO launched by the ESA in 1995 and the life expectancy of which was of 28 months. The launch of the telescope was made by a rocket Delta II, on August 25th, 2003 on the Cap Canaveral in Florida. Before his launch, he was named SIRTF for Space Infrared Telescope Facility but was reappointed Spitzer, of the name of an American scientist, Lyman Spitzer.
He can observe and detect the infrared radiation emitted by objects in wavelengths between three and hundred sixty micrometers.
He can make approximately 100 000 observations during his life, the forecast of which is of 5 years.
Its unique orbit will allow its to use the cold temperatures of the space for its cooling (besides that supplied by 400 liters of liquid helium) and its solar panels will bring its the energy and will protect it from solar emissions (radiation and particles).
The new very sensitive instruments of the telescope will allow to drill the space which is darkened by clouds of gas, the interstellar clouds which block telescopes working in the visible domain.
It already brings new data about the formation of planets as well as on cold objects such as the brown dwarfs, and the infrared galaxies, the seats of formation of very intense star.
The spatial telescope Hubble (Hubble Space Telescope or HST) is a telescope in orbit in approximately 560 kilometers in height, it makes a complete tour of the Earth every 100 minutes. It is named in honor of the astronomer Edwin Hubble Edwin Powell Hubble (in 20/11/1889 - 28/09/1953) American astronomer who showed that the Universe is expanding. Hubble is is born to Marshfield in the Missouri. He studies the mathematics and the astronomy to the university of Chicago where he) obtains his diploma in 1910. Holder of a scholarship, he crosses then 3 years to the university of Oxford where he obtains Master of Arts there straight ahead. He quickly returns to the astronomy to the look-out observatory Yerkes, where he receives his Ph. D. in 1917. Drag, the founder and the director of the observatory of the Mountain Wilson, near Pasadena in California, proposes him researcher's post. He pursues his works till the end of his life there On 28/09/1953.. Its launch The telescope was launched on April 25th, 1990 by the mission STS-31 of the Space shuttle Discovery. This launch had already been delayed in 1986 because of the disaster of the space shuttle Challenger in January of this year., made April 25th, 1990 by a Space shuttle, is the fruit of a common project between the NASA and the ESA. This telescope has an optical resolution better than 0,1 assist of bow. It is planned to replace Hubble Space Telescope in 2018 by the James Webb Space Telescope (previously named spatial Telescope new generation, Next Generation Space Telescope or NGST). The telescope Hubble weighs approximately 11 tons, is 13,2 meters long, has a maximum diameter of 4,2 meters and cost 2 billion US dollars. It is a telescope reflector in two mirrors; the main mirror is one diameter 2,4 meters.
It is coupled with diverse spectrometers and three cameras: one in narrow field for the weakly brilliant objects, the other one in wide field for the global images and one for the infrared. It employs two solar panels to produce some electricity, which is mainly used by cameras and four big steering wheels used to direct and stabilize the telescope.
The infrared camera and the spectrometer multi-objects must be also cooled in 180 °C. The first images supplied by the telescope were generally considered as very disappointing by the astronomers and all those concerned by the project. These images were vague and, in spite of the treatment of image, did not reach the foreseen resolution. Since then, the most beautiful images of the Universe come from Hubble. Hubble is a powerful "machine to go up time" that allows astronomers to see galaxies as they were there 13 billion years ago, just 600 million to 800 million years after the Big Bang. These data are essential to understand the universe as we now observe. The Hubble Space Telescope has been repaired for the last time in May 2009, maintenance was to extend its life of 5 years. To do this, astronauts went repair ACS camera and imaging spectrometer STIS, change 6 gyroscopes, communications systems and storage and put new batteries. Two new instruments are installed, a wide field camera and a new spectrometer to increase the visual acuity. A docking mechanism was also installed to deorbit the telescope at the end of life.
PAMELA (Payload for Antimatter Exploration and Light-nuclei Astrophysics) is a observatory in orbit intended to determine the characteristics of the black matter.
The researchers in search of antimatter in the universe appeal to detectors embarked aboard spatial machines, such as PAMELA or AMS (modulate for the ISS, the international space station).
Pamela was launched on June 15th, 2006 by a Russian rocket aboard a satellite Resurs DK1.
It will be the most complex detector of particles never launched in the space because he can detect and measure with an exceptional precision the load, the mass and the specter of energy of the cosmic particles which will strike its detector.
The objective is to study the cosmic particles, their specter, their origin, the presence of antiparticles, and the possible presence of black matter.
The European spatial telescope of the European Space agency ( E.S.A). XMM-Newton was launched on December 10th, 1999. It is the biggest observatory with X-rays never built. After one year of activity, the biggest observatory with X-rays never built delivers an impressive variety of scientific results. XMM-Newton allowed to discover of new heap of galaxies to considerable distances, several billion light years.
This project aims at determining the distribution of the heap of galaxies in the distant Universe and at confronting it with the predictions of the models of evolution of the Universe.
The Universe does not appear as a distribution of matter distributed in a uniform way but more as a set of strands constituted by galaxies gathering in the knots of these strands to form heap of galaxies.
They can contain thousands of galaxies, and their mass can reach a million billion times ( 1014 ) the mass of the Sun. The study of the formation of these heap, an important detail of the puzzle of the structure of the Universe, is at the same moment the object of numerous programs of observations and numeric simulations. But track down in the visible distant domain of the heap to reconstitute the puzzle of their formation raise very severe problems of observations because of the extreme weakness of the light signal reaching us.
Another technique, the observation in the field of the X-rays, is possible.
Indeed, a not unimportant fraction (approximately 20) of the mass of a heap is constituted by a diffuse warm gas, situated between the galaxies. This gas is warmed, considering the high gravitational potential, in temperatures which could reach to reach several tens of million degrees. A gas raised to such temperatures is a powerful source of radiation X. The strategy adopted by the international team within the framework of the program baptized "Poll of the structure with large scales with XMM" thus consists first of all in detecting the emission X of this warm gas and to look for by imaging in the same region of the sky the optical counterparts.
The distances of the galaxies constituting the heap are finally determined thanks to spectroscopic measures. The imaging is led indeed has by using the telescope of 3,6 m of the observatory (CFHT) Canada-France-Hawaii whereas the spectroscopic measures are led to one of the huge telescopes of the European observatory of the VLT. The extraordinary sensibility of the satellite XMM-Newton bound to the power of the means of observation on the ground operating in the visible domain so allows a considerable headway in the understanding of the formation of the heap distant and of the structure of the Universe.
The Herschel satellite is equipped with a telescope 3.5 meters in diameter and weighs 3300 kg dimension of 9m x 4m x 4m. He observed the universe in the far infrared and submillimeter wave fields in 55 microns to 670 microns in length, a window of the electromagnetic spectrum poorly explored. It was an opportunity to study the formation of galaxies and stars. Detectors traditionally used for imaging in this wavelength range are bolometers.
These detectors measure the intensity of infrared radiation by the rise in temperature of an absorbent material. The Astrophysical Service (SAp) at CEA-DAPNIA has participated in the production of scientific instruments on board the Herschel Space Observatory of the European Space Agency (ESA). The launch by Ariane 5 rocket, scheduled for 2007 took place on 14 May 2009 on the launch pad in French Guiana. The Planck spacecraft is part of the journey. On July 3, 2009, Planck has reached the L2 Lagrange point and was placed on a course called Lissajous orbit. The images taken by Herschel showed complex networks of filaments of dust and gas in our galaxy. These exceptional observations in the far infrared astronomers provide new insights into how the turbulence wave the gas in the interstellar medium and give rise to filamentary structures present in cold molecular clouds. Herschel could include the presence of water molecule crucial for life as we know it in clouds containing forming stars, and disks containing planets.
April 29, 2013, after exhausting its 2,300 liters of cooling liquid (helium), Herschel completed his observations of the cold Universe mission. "Herschel has exceeded our expectations by providing us with an extraordinary wealth of data that will occupy astronomers for many years," said Prof. Alvaro Giménez, Director of Science and Robotic Exploration ESA.
Herschel has performed over 35,000 scientific observations. These records are stored at the European Space Astronomy Centre of ESA, near Madrid, Spain. "Herschel has given us an entirely new view of the universe, showing us things that we were hidden, as never seen before process of star birth and galaxy formation, and helping us to detect the presence of water throughout the universe, in molecular clouds like the new stars and their protoplanetary disks and belts comets, "says Göran Pilbratt, Herschel Project scientist at ESA. In May 2013, Herschel was propelled on a scrap steady orbit around the Sun where it will remain for the long term.
NB: The Lagrangian points: the L2 point, the object orbits the Sun at the same angular velocity as the Earth. A satellite on one of these points do not move any more and turned together, permanently, with the Earth around the Sun. On this point is since June 2001, the WMAP (Wilkinson Microwave Anisotropy Probe) and in 2011 the James Webb Space Telescope will join them.
The Planck space observatory of ESA captures the cosmic radiation or cosmic microwave background (CMB). The CMB is the "first light" of the material world, published shortly after the Big Bang, there 13,800,000,000 years ( ≈ 1%), when the light began to travel freely for the first time. The gigantic fireball that followed the Big Bang is slowly cooled to become a backdrop of microwaves. Planck observes and measures the temperature variations across this microwave background, with a much higher sensitivity, better angular resolution and a wider range of frequencies than any previous observatories. Planck showed us what it is like Universe through the first light emitted when it was at a temperature of 3000 ° C and was only 380,000 years. On July 3, 2009, Planck has reached the L2 Lagrange point and was placed on a course called Lissajous orbit. Planck, the time machine measure with high accuracy the cosmic background radiation or cosmic microwave background (trace of the Big Bang ) to establish a mapping of inhomogeneities of temperature and polarization of the radiation.
For this he has a telescope of 1.5 m diameter and 2 scientific instruments developed by the LFI and HFI Italy entrusted to France. The first promising images, arrived June 14, 2009. This is the famous image of the spiral Whirlpool Galaxy, M51, that those responsible for the instrument Photoconductor Array Camera and Spectrometer have received for a first analysis. The first edition of the catalog of compact sources ( ERCSC, Early Release Compact Source Catalogue) was published and presented on 11 January 2011, with thousands of sources detected by Planck. The reserve of helium used to cool ran out in January 2012 and October 2013, the operations center of the European Space Agency (ESA), based in Darmstadt (Germany), turned off the transmitters and instruments satellite. But for scientists there is still much data to analyze. In 2014, they will publish a new set of cosmological data. Then the Planck satellite will be powered on a scrap steady orbit around the Sun where it will remain forever, along with the Herschel satellite. The two satellites were launched together by an Ariane rocket in May 2009.
The spatial telescope MOST (Microvariability and oscillation of STARS or Microvariability and Oscillation of Stars) is launched in the space in 2003. It is the first Canadian scientific satellite sent into orbit and completely conceived and built by Canada.
MOST is a small telescope dedicated only to the asterosismology, that is to the study of the vibrations which shake stars. The interest to study such vibrations is big because he allows to obtain information on the internal structure of a star, thus, on his dimensions, his mass and his constituents. The project is introduced in 1996 by the researchers Slavek Rucinski of the Research center in Technologies of the Earth and the Space of Ontario, Jaymie Matthews and Tony Moffat. Of the size and the shape of a big suitcase, the satellite weighs only 54 kilograms and is endowed with a telescope sophisticated extreme reactionary of hardly 15 centimeters in diameter. Nevertheless, it is ten times as sensitive as the spatial telescope Hubble to detect the tiny variations of luminosity of stars due to the vibrations which shake their surface. MOST makes a complete orbit around the Earth every 101 minutes by way of both poles of the Earth.
He can so cross 60 days to observe continuously the same star. Its life cycle should be from 5 to 10 years old.
The first major discovery is made in 2004 concern Procyon, one of the stars the most studied by the astronomers. While we expect to see the celestial body vibrating, we notice that it is nothing.
It contradicts 20 years of theories and observations so forcing the astrophysicists to rethink their models on stars. In 2005, MOST observes for the first time a huge planet which orbits if near its star host that this one sees itself forced to synchronize its rotation with the planet. Usually, it is the planets which synchronize their rotation with their star.
SOHO mission aims to study the internal structure of the Sun, its warm atmosphere, the origins of the solar wind. The SOHO spacecraft is a collaboration between NASA and ESA. It was launched on 2 December 1995 based on Cape Canaveral (USA) by a rocket Atlas II. In operation since February 1996, and despite a loss of contact for several months, the mission is going remarkably well and is extended beyond 2010. The Earth-Sun distance is 150 million kilometers. SOHO operates in a halo orbit around the Lagrange point L1. At this point, the gravitational forces exerted by the Sun and the Earth on an object are balanced, but the balance is unstable and therefore SOHO orbits around this particular point. SOHO period is equal to the period of revolution of the Earth around the Sun, or about 365 days. December 26, 2010 SoHo (Solar and Heliospheric Observatory) discovered its 2000th comet. It belongs to the group of comets " Kreutz", a large population of comets that all share the same orbital path in space. Kreutz comets come from a single parent comet has probably broken near the Sun there for centuries or more. Approximately 85% of the comets SOHO finds are tiny fragments of the original object.
Kepler, the Space Telescope over a ton, went toward the Milky Way, 6 March 2009 to 22 h 48 hours of Florida, aboard a Delta II, searching for extrasolar planets or exoplanets.
The planets that Kepler telescope will look, are exoterres small sizes, 2 to 20 times the size of Earth, they can not see that Corot.
In March 2009, scientists say they have discovered 342 extrasolar planets, 289 stars with planets planets and 0 identical to the size of Earth.
The 342 planets are gas giants for the most part, but none in the habitable zone.
It is to achieve this goal the Americans have launched Kepler mission, designed to determine whether habitable planets outside our solar system.
Kepler will look closely for three and a half years, more than 100 000 stars in the Milky Way, rather in the regions of Cygnus and Lyra.
It will detect planets orbiting stars similar to our Sun, rocky like our Earth and also positioned in the habitable zone, i.e. neither too far nor too near its star.
Kepler telescope embarks on this specialty meter in diameter with a field of vision of 105 degrees and an image resolution of 95 megapixels.
This monster of NASA sees broad as it is equipped with a photometer to measure the brightness of tens of thousands of stars simultaneously, to increase the chances of discovery by the transit method.
A transit occurs whenever a planet passes between its star and the observer at that time, the planet obscures some of the starlight, producing a detectable periodic dimming.
This signature is used to detect the planet and determine its size and its orbit.
"Kepler mission, for the first time, will enable humans to search for galaxy-sized planets similar to Earth or even smaller," said principal investigator William Borucki Research Center of NASA, California .
"With its advanced capabilities, Kepler will help us answer one of the oldest questions in human history: Are there other things that we in the universe?"
Space Telescope (WISE Widefield Infrared Survey Explorer) is a satellite carrying an infrared telescope designed to photograph sensitive across the entire sky. Its primary objective is to detect the infrared asteroids in the solar system and of course the Near Earth Objects whose trajectory is likely to graze the Earth. Its second objective is to detect young stars or low light in the vicinity of the Sun which are difficult to observe brown dwarfs because it does not shine. Its third objective is to detect the stars of our galaxy obscured by interstellar clouds. These invisible stars, constitute more than 90% of all stars. And finally to observe the structure and process of formation of nearby galaxies. As the observations in the infrared are sensitive to temperature, the telescope WISE and its detectors are kept at very cold temperatures (258 º C, only 15 ° Celsius above absolute zero) by a cryostat filled with solid hydrogen instead ice.
Solar panels that always point toward the Sun, which provide electricity for the spacecraft needs to operate. WISE is in orbit above the dividing line between night and day on Earth, the telescope is on a right angle to the sun and Earth.
The orbits of WISE, aligned to the North Pole to South Pole through the equator, can scan a strip of sky. As the Earth moves around the Sun, the band swept the sky, and after six months WISE has observed the entire sky.
WISE captures an image of the sky every 11 seconds. Each image covers an area of the sky 3 times larger than the full Moon. Every 6 months, WISE takes nearly 1 500 000 pictures to cover the entire celestial dome. Each photo is taken on four different wavelengths.
The data taken by WISE are sent by radio transmission, 4 times a day and downloaded on computers to gather images that will produce an atlas covering the whole celestial sphere.
ESA's Earth Explorer CryoSat mission is dedicated to precise monitoring of changes in the thickness of floating sea ice in polar oceans, and variations in the thickness of the ice cap covering Greenland and Antarctica. The effects of climate change are much more visible in the polar regions, it is important to understand exactly how the ice fields of the Earth react.
The decrease in ice cover is often cited as an early victim of global warming and polar ice plays an important role in regulating climate and sea levels. The CryoSat-2 satellite was launched into orbit Thursday, April 8, 2010 by Dnepr rocket launched from Kazakhstan, CryoSat-2 will follow the variations in the height of the ice in the polar regions, with millimeter precision. Thanks to the altimeter and the help of Doris, the satellite CryoSat-2 will measure variations in the height of the ice. "After the failed launch of CryoSat-1 in 2005, it was decided very quickly to a new satellite to observe the ice, said Francoise Schiavon, project leader at CNES CryoSat-2.
The satellite, orbiting polar ice caps fly regularly for 3 years until 2013. Each time, the altimeter will measure the height of the ice of Antarctica and the Arctic but also that of sea ice and mountain glaciers.
For bumpy areas, like the edges of the Antarctic glaciers, take 2 altimeter measurements at 2 different angles to get information on the terrain. The CryoSat-2 will fly over the Earth at an altitude of just over 700 km, reaching latitudes of 88 °.
"All data will be archived by the CNES will be capable of generating altimetric products demand," said Francoise Schiavon. In responding to this challenge, data from the CryoSat mission will help us understand how climate changes affect these areas and lead to a better understanding of the role ice plays in the Earth system.
Launched February 11, 2010, SDO is the most sophisticated spacecraft ever designed to study the sun. After a series of small adjustments to the engine, SDO has stabilized in geosynchronous orbit.
During his five-year mission, the Space Telescope will examine the Sun's magnetic field leading to a better understanding of the role the sun plays on the Earth's atmospheric chemistry and climate.
Since its launch, the engineers have done for 2 months, testing and verification of components.
Fully operational in April 2010, SDO will provide images with a clarity 10 times better than HDTV.
Data were available from a variety of settings including turning on the Ka-band transmitter, which allowed the instrument to begin its scientific observations from mid-May 2010. During the mission, engineers will collect scientific data more complete and faster than any other solar observing spacecraft. SDO is designed to help us understand the Sun's influence on Earth and Earth space and study of the solar atmosphere will be in several wavelengths simultaneously. SDO has 10 CCDs with eight inside and two scientific instruments in the star trackers. CCD sensors can operate at very low temperatures down to -100 ° C. These high-quality CCD sensors in visible light are designed for the detection of extreme ultraviolet light. They are cooled and protected from the sun by a panel radiators. The thermal radiation of the panel is sufficient to send into space the small amount of heat generated by the use of CCD sensors. The exceptional activity of the Sun of April 5, 2010 has affected our satellite fleet.
The Galaxy 15 satellite stopped responding to commands and engineers undertake the recovery operation.
NB: The geosynchronous orbit, or GSO (geosynchronous orbit), is a geocentric orbit of a satellite which moves in the same direction as the Earth (from west to east) and whose orbital period is equal to the sidereal rotation period of land (about 23h 56min 4.1 s). This orbit has a semi-major axis of about 42 200 km. If the orbit is located in the plane of the equator, the satellite appears as a fixed point in the sky.
It is then called "geostationary orbit". The geostationary orbit is a geosynchronous orbit that has a zero inclination and eccentricity.
If the orbit is inclined to the plane of the equator, the satellite describes an analemma in the sky when viewed from a fixed point on the surface of the Earth.
SWIFT is a space telescope, launched on a low Earth orbit, November 20, 2004 at 5:16:00 p.m. UTC, by a Delta 2 rocket. The purpose of SWIFT is to study gamma-ray bursts. Gamma-ray bursts (GRBs) are explosions, the most powerful of the Universe since the Big Bang. Gamma-ray bursts, brief but intense, occur about once a day in the universe. These are real hot burning of gamma radiation coming from all directions of the sky and last from a few milliseconds to a few hundred seconds. Scientists wonder if these are births of black holes, stellar explosions, collisions of neutron stars, dislocations of stars by a supermassive black hole, or is it another exotic phenomenon that causes these explosions?
SWIFT is a NASA mission with international participation.
Since 2004, scientists have a dedicated tool to answer these questions and solve the mystery of gamma-ray burst. Its three scientific instruments provide the opportunity to scrutinize gamma-ray bursts like never before. Within seconds of detecting a burst, Swift relays its location cosmic ground stations, allowing both ground-based telescopes and spacecraft from around the world to observe the burst afterglow.
Probe Wilkinson Microwave Anisotropy Probe (WMAP) was launched June 30, 2001. It is intended to study the anisotropy i.e. the study of the CMB (Cosmic Microwave Background). WMAP was named in tribute to the American astronomer David Wilkinson, member of the team in charge of the satellite, a pioneer in the study of cosmic microwave background, who died Sept. 5, 2002. The purpose of the mission is to map the best possible accuracy with the temperature fluctuations of the cosmic microwave thermal radiation and its polarization to allow recovery of the material content of the universe. The first results of the WMAP probe have been rightly hailed as a breakthrough in understanding the universe because WMAP produced the first complete map of the CMB from that of the COBE satellite in 1992 and it has a resolution significantly better. The cosmos is older than 13.7 billion years. The first generation of stars began to light up 200 million years after the Big Bang. The image was published February 11, 2003. This picture shows a map of the observable universe known in the state it was in his establishment, at the age of 380 000 years as it became transparent.
This murmur radio captured in the 3K radiation or -270°C, shows the residual fluctuations of our universe and filigree, lumps of matter that gave rise to galaxies. Planck Space Observatory, launched in May 2009 takes over to explain the history of the Universe. Its objective is to observe the cosmic microwave background, the radiation emitted 380,000 years after the birth of the universe, which explains why the current temperature of the Universe is 2.7 K.
"By observing this signal, we can go back in time and see the universe as it was there billions of years ago," explains Dominique Yvon, astrophysicist at the CEA. The age of the universe has been clarified by observations of the WMAP probe.
Cosmological parameters indicate a probable value for the age of the universe about 13.7 billion years with an uncertainty of 0.2 billion years.