̽��ֱ�� of Cambridge - ̽��ֱ�� of Liege

New details of TRAPPIST-1 system’s outermost planet confirm earlier predictions

sc604 — Mon, 22 May 2017 15:00:00 +0000

̽��ֱ��observations confirm, as had been predicted, that the seventh and outermost planet, TRAPPIST-1h, orbits its star every 18.77 days. ̽��ֱ��results are reported in the journal Nature Astronomy.

“TRAPPIST-1h was exactly where our team predicted it to be,” said Rodrigo Luger, a PhD student at the ̽��ֱ�� of Washington and the paper’s lead author. ̽��ֱ��researchers discovered a mathematical pattern in the orbital periods of the inner six planets, which was strongly suggestive of an 18.77 day period for planet h.

TRAPPIST-1A is a middle-aged, ultra-cool dwarf star, much less luminous than the Sun and only a bit larger than Jupiter. ̽��ֱ��star, which is nearly 40 light years away in the constellation of Aquarius, is named after the ground-based Transiting Planets and Planetesimals Small Telescope (TRAPPIST), the facility that first found evidence of planets around it in 2015.

̽��ֱ��TRAPPIST survey is led by Michaël Gillon of the ̽��ֱ�� of Liège, Belgium, who is also a co-author on this research. In 2016, Gillon’s team announced the detection of three planets orbiting TRAPPIST-1 and this number was upped to seven in a paper published earlier this year. All seven planets are deemed temperate, meaning that under certain geologic and atmospheric conditions, water could exist in a liquid form. Three of the planets are particularly optimal. In addition the TRAPPIST-1 system is currently the most convenient to remotely explore the atmospheres of planets with sizes similar to Earth.

Such exoplanets are detected when they transit, or pass in front of, their host star, blocking a measurable portion of the light. “We only captured one transit of TRAPPIST-1h last autumn. However, the resonant pattern formed by the other six planets, and the time TRAPPIST-1h takes to pass in front of its star, allowed the team to deduce its orbital period with a precision of a few minutes,” said co-author Amaury Triaud, a Kavli Exoplanet fellow Amaury Triaud at Cambridge’s Institute of Astronomy. “This is absolutely remarkable! TRAPPIST-1h represents a perfect illustration of the power of the scientific method, of its ability to make predictions that can later be verified.”

̽��ֱ��inner six planets occupy orbits consistent with being in ‘resonance’. All orbital periods are mathematically related and slightly influence each other. Orbital resonances can also be found in our solar system. For instance, Jupiter’s moons Io, Europa and Ganymede are set in a 1:2:4 resonance, meaning that while Ganymede orbits Jupiter once, Europa does so twice, and Io four times. ̽��ֱ��prediction of TRAPPIST-1h’s orbital period principally relied on extrapolating the known resonant configuration of the inner six planets, to the seventh. This prediction was later confirmed.

̽��ֱ��team analysed 79 days of observation data from K2, the second mission of the Kepler Space Telescope, and was able to recover four transits of TRAPPIST-1h across its star. ̽��ֱ��K2 data was also used to further characterize the orbits of the other six planets, help rule out the presence of additional transiting planets, and learn the rotation period and activity level of the star.

TRAPPIST-1's seven-planet chain of resonances establishes a record among known planetary systems. ̽��ֱ��resonances strengthen the long-term stability of the planetary system. It is also likely that these orbital connections were forged early in the life of the TRAPPIST-1 system, when the planets and their orbits were not fully formed.

“Observing TRAPPIST-1 with K2 was an ambitious task,” said Marko Sestovic, a PhD student at the ̽��ֱ�� of Bern and second author of the study. In addition to the complicated signals introduced by the spacecraft’s wobble, the faintness of the star in the optical (the range of wavelengths where K2 observes) placed TRAPPIST-1h “near the limit of what we could detect with K2,” he said. To make matters worse, Sestovic said, one transit of the planet coincided with a transit of TRAPPIST-1b, and one happened during a stellar flare, adding to the difficulty of the observation. “Finding the planet was really encouraging,” Luger said, “since it showed we can still do high-quality science with Kepler despite significant instrumental challenges.”

̽��ֱ��research was funded by the NASA Astrobiology Institute via the UW-based Virtual Planetary Laboratory as well as a National Science Foundation Graduate Student Research Fellowship, the Swiss National Science Foundation, the European Research Council and the UK Science and Technology Facilities Council, among other agencies. This work was partially supported by a grant from the Simons Foundation.

Based on a press release by the ̽��ֱ�� of Washington.

Reference:
Rodrigo Luger et al. 'A seven-planet resonant chain in TRAPPIST-1.' Nature Astronomy (2017). DOI: 10.1038/s41550-017-0129

An international team of astronomers, including researchers from the ̽��ֱ�� of Cambridge, used data gathered by the Kepler Space Telescope to observe and confirm details of the outermost of seven exoplanets orbiting the star TRAPPIST-1.

TRAPPIST-1h represents a perfect illustration of the power of the scientific method, of its ability to make predictions that can later be verified.

Amaury Triaud

IoA/Amanda Smith

Artist's impression of TRAPPIST-1

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Newly discovered planets could have water on their surfaces

ps748 — Wed, 22 Feb 2017 13:09:42 +0000

̽��ֱ��team has been using the TRAPPIST–South telescope at the European Southern Observatory’s (ESO) La Silla Observatory, the Very Large Telescope (VLT) at Paranal, the NASA Spitzer Space Telescope as well as two other telescopes supported by the UK’s STFC, the William Herschel Telescope and the Liverpool Telescope. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes comparable to Earth.

̽��ֱ��astronomers identified the planets thanks to periodic drops in the brightness of the central star. As the planets passed in front of the star, they cast a shadow, events known as transits, from which the team could measure the planet’s orbital periods and calculate their sizes and masses. They found that the inner six planets were comparable in size, mass and temperature to the Earth raising the possibility that they host liquid water on their surface.

With just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms, only marginally bigger than the planet Jupiter — and though nearby in the constellation Aquarius, it is invisible visually with anything less than powerful telescopes. Astronomers expected that such dwarf stars might host many Earth-sized planets in tight orbits, making them promising targets in the hunt for extraterrestrial life. TRAPPIST-1 is the first such system to be discovered.

Co-author Dr Amaury Triaud, of the ̽��ֱ�� of Cambridge’s Institute of Astronomy, explains: “Stars like TRAPPIST-1 belong to the most common type of stars that exist within our Galaxy. ̽��ֱ��planets that we found are likely representative of the most common sort of planets in the Universe.

“That the planets are so similar to Earth bodes well for the search for life elsewhere. Planets orbiting ultra-cool dwarfs, like TRAPPIST-1, likely represent the largest habitable real estate in the Milky Way!”

̽��ֱ��seven planets of the TRAPPIST-1 system. Credit: ESO

̽��ֱ��team determined that all the planets in the system were similar in size to Earth and Venus in our Solar System, or slightly smaller. ̽��ֱ��density measurements suggest that at least the innermost six are probably rocky in composition.

̽��ֱ��planetary orbits are not much longer than that of Jupiter’s Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1’s small size and low temperature means that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar energy inputs to Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. ̽��ֱ��orbital distance of the system’s outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water — assuming no alternative heating processes are occurring. TRAPPIST-1e, f, and g, however, are of more interest for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of surface water.

These new discoveries make the TRAPPIST-1 system an even more important target in the search for extra-terrestrial life. Team member Didier Queloz, from the ̽��ֱ�� of Cambridge’s Cavendish Laboratory, is excited about the future possibilities: “Thanks to future facilities like ESO’s Extremely Large Telescope, or NASA/ESA’s soon-to-be-launched James Webb Space telescope, we will be capable to measure the structure of the planets’ atmospheres, as well as their chemical composition. We are about to start the remote exploration of terrestrial climates beyond our Solar system.”

̽��ֱ��discovery is described in Nature, which also includes a science fiction short story, written by Laurence Suhner. Amaury Triaud comments: “We were thrilled at the idea of having artists be inspired by our discoveries right away. We hope this helps convey the sense of awe and excitement that we all have within the team about the TRAPPIST-1 system.”

̽��ֱ��star draws its name from the TRAPPIST-South telescope, which made the initial discovery. TRAPPIST is the forerunner of a more ambitious facility called “SPECULOOS” that includes Cambridge as core partner, conducted by researchers of the “Cambridge Centre for Exoplanet Research” in the broad research context related to “Universal Life”. SPECULOOS is currently under construction at ESO’ Observatory of Cerro Paranal. SPECULOOS will survey 10 times more stars for planets, than TRAPPIST could do. We expect to detect dozens of additional terrestrial planets.

Michaël Gillon et al: “Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1” Nature 23rd Feb. 2017

http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html

Link to a science-fiction short story: http://www.nature.com/nature/journal/v542/n7642/full/542512a.html

Cambridge Exoplanet Research Centre: http://exoplanets.phy.cam.ac.uk

For additional information, images, videos, a graphic novel and short stories, visit www.trappist.one

Adapted from a press release by the European Southern Observatory (ESO)

An international team of astronomers has found a system of seven potentially habitable planets orbiting a star 39 light years away three of which could have water on their surfaces raising the possibility they could host life. Using ground and space telescopes, the team identified the planets as they passed in front of the ultracool dwarf star known as TRAPPIST-1. ̽��ֱ��star is around eight per cent of the mass of the Sun and is no bigger than Jupiter.

That the planets are so similar to Earth bodes well for the search for life elsewhere

Amaury Triaud

Seven Earths FinalYT1

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Three potentially habitable worlds found around nearby ultracool dwarf star

sc604 — Mon, 02 May 2016 19:02:00 +0000

An international team of astronomers has discovered three planets orbiting an ultracool dwarf star just 40 light years from Earth. These worlds have sizes and temperatures similar to those of Venus and Earth and may be the best targets found so far for the search for life outside the Solar System. They are the first planets ever discovered around such a tiny and dim star. ̽��ֱ��results are reported in the journal Nature.

Using the TRAPPIST telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile, the astronomers observed the star 2MASS J23062928-0502285, now also known as TRAPPIST-1, and located in the Aquarius constellation. They found that this dim and cool star faded slightly at regular intervals, indicating that several objects were transiting, or passing between the star and the Earth. Detailed analysis showed that three planets with similar sizes to the Earth were present.

TRAPPIST-1 is an ultracool dwarf star — much cooler and redder than the Sun and barely larger than Jupiter. Such stars are very common in the Milky Way and very long-lived, but this is the first time that planets have been found around one of them. Despite being so close to the Earth, this star is too dim and too red to be seen with the naked eye or even with a large amateur telescope.

“ ̽��ֱ��discovery of a planetary system around such a small star opens up a brand new avenue for research,” said Professor Didier Queloz from the ̽��ֱ�� of Cambridge’s Cavendish Laboratory, the paper’s senior author. “Before this discovery it was not at all clear whether such a small star could host an Earth-sized planet. Nobody had seriously studied it, but now that’s likely to change.”

“Systems around these tiny stars are the only places where we can detect life on an Earth-sized exoplanet with our current technology,” said the paper’s lead author Michaël Gillon, from the ̽��ֱ�� of Liège in Belgium. “So if we want to find life elsewhere in the Universe, this is where we should start to look.”

Astronomers will search for signs of life by studying the effect that the atmosphere of a transiting planet has on the light reaching Earth. For Earth-sized planets orbiting stars similar to our Sun this tiny effect is swamped because of the large size ratio between the planet and the star. Only for the case of faint red ultra-cool dwarf stars — like TRAPPIST-1 — is this effect big enough to be detected.

Follow-up observations with larger telescopes have shown that the planets orbiting TRAPPIST-1 have sizes very similar to Earth. Two of the planets complete an orbit of the star in 1.5 days and 2.4 days respectively, and the third planet has a less well determined orbital period in the range of 4.5 to 73 days.

“With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun,” said Gillon. “ ̽��ֱ��structure of this planetary system is much more similar in scale to the system of Jupiter’s moons than to that of the Solar System.”

Although they orbit very close to their host dwarf star, the inner two planets only receive four and two times, respectively, the amount of radiation received by the Earth, because their star is much fainter than the Sun. That puts them closer to the star than the habitable zone for this system. ̽��ֱ��third, outer, planet’s orbit is not yet well known – it probably receives less radiation than the Earth does, but perhaps still enough to lie within the habitable zone.

̽��ֱ��next generation of giant telescopes, such as NASA’s James Webb Telescope due to launch in 2018, will allow researchers to study the atmospheric composition of these planets and to explore them first for water, and then for traces of biological activity.

“While this is not the first time that planets have been found in the habitable zone of a star, the TRAPPIST-1 system provides humanity with our first opportunity to remotely explore Earth-like environments and empirically determine their suitability for life,” said study co-author Dr Amaury Triaud from Cambridge’s Institute of Astronomy. “Because the system contains many planets, we will even be able to compare the climates of each to one another and to the Earth’s.”

This work opens up a new direction for exoplanet hunting, as around 15% of the stars near to the Sun are ultra-cool dwarf stars, and it also serves to highlight that the search for exoplanets has now entered the realm of potentially habitable cousins of the Earth. ̽��ֱ��TRAPPIST survey is a prototype for a more ambitious project called SPECULOOS that will be installed at ESO’s Paranal Observatory in Chile.

Reference:
Michaël Gillon et al. ‘Temperate Earth-sized planets transiting a nearby ultracool dwarf star.’ Nature (2016). DOI: 10.1038/nature17448

Adapted from an ESO press release.

Three Earth-sized planets have been discovered orbiting a dim and cool star, and may be the best place to search for life beyond the Solar System.

̽��ֱ��discovery of a planetary system around such a small star opens up a brand new avenue for research.

Didier Queloz

ESO/M. Kornmesser

Artist’s impression of the ultracool dwarf star TRAPPIST-1 from the surface of one of its planets.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Astronomers find first evidence of changing conditions on a super Earth

sc604 — Mon, 04 May 2015 23:01:20 +0000

For the first time, researchers led by the ̽��ֱ�� of Cambridge have detected atmospheric variability on a rocky planet outside the solar system, and observed a nearly threefold change in temperature over a two year period. Although the researchers are quick to point out that the cause of the variability is still under investigation, they believe the readings could be due to massive amounts of volcanic activity on the surface. ̽��ֱ��ability to peek into the atmospheres of rocky ‘super Earths’ and observe conditions on their surfaces marks an important milestone towards identifying habitable planets outside the solar system.

Using NASA’s Spitzer Space Telescope, the researchers observed thermal emissions coming from the planet, called 55 Cancri e – orbiting a sun-like star located 40 light years away in the Cancer constellation – and for the first time found rapidly changing conditions, with temperatures on the hot ‘day’ side of the planet swinging between 1000 and 2700 degrees Celsius.

“This is the first time we’ve seen such drastic changes in light emitted from an exoplanet, which is particularly remarkable for a super Earth,” said Dr Nikku Madhusudhan of Cambridge’s Institute of Astronomy, a co-author on the new study. “No signature of thermal emissions or surface activity has ever been detected for any other super Earth to date.”

Although the interpretations of the new data are still preliminary, the researchers believe the variability in temperature could be due to huge plumes of gas and dust which occasionally blanket the surface, which may be partially molten. ̽��ֱ��plumes could be caused by exceptionally high rates of volcanic activity, higher than what has been observed on Io, one of Jupiter’s moons and the most geologically active body in the solar system.

“We saw a 300 percent change in the signal coming from this planet, which is the first time we’ve seen such a huge level of variability in an exoplanet,” said Dr Brice-Olivier Demory of the ̽��ֱ��’s Cavendish Laboratory, lead author of the new study. “While we can’t be entirely sure, we think a likely explanation for this variability is large-scale surface activity, possibly volcanism, on the surface is spewing out massive volumes of gas and dust, which sometimes blanket the thermal emission from the planet so it is not seen from Earth.”

55 Cancri e is a ‘super Earth’: a rocky exoplanet about twice the size and eight times the mass of Earth. It is one of five planets orbiting a sun-like star in the Cancer constellation, and resides so close to its parent star that a year lasts just 18 hours. ̽��ֱ��planet is also tidally locked, meaning that it doesn’t rotate like the Earth does – instead there is a permanent ‘day’ side and a ‘night’ side. Since it is the nearest super Earth whose atmosphere can be studied, 55 Cancri e is among the best candidates for detailed observations of surface and atmospheric conditions on rocky exoplanets.

Most of the early research on exoplanets has been on gas giants similar to Jupiter and Saturn, since their enormous size makes them easier to find. In recent years, astronomers have been able to map the conditions on many of these gas giants, but it is much more difficult to do so for super Earths: exoplanets with masses between one and ten times the mass of Earth.

Earlier observations of 55 Cancri e pointed to an abundance of carbon, suggesting that the planet was composed of diamond. However, these new results have muddied those earlier observations considerably and opened up new questions.

“When we first identified this planet, the measurements supported a carbon-rich model,” said Madhusudhan, who along with Demory is a member of the Cambridge Exoplanet Research Centre. “But now we’re finding that those measurements are changing in time. ̽��ֱ��planet could still be carbon rich, but now we’re not so sure – earlier studies of this planet have even suggested that it could be a water world. ̽��ֱ��present variability is something we’ve never seen anywhere else, so there’s no robust conventional explanation. But that’s the fun in science – clues can come from unexpected quarters. ̽��ֱ��present observations open a new chapter in our ability to study the conditions on rocky exoplanets using current and upcoming large telescopes.”

̽��ֱ��results have been published online today.

̽��ֱ��study was also co-authored by Professor Didier Queloz of the Cavendish Laboratory and Dr Michaël Gillon of the Université of Liège.

Astronomers have detected wildly changing temperatures on a super Earth – the first time any atmospheric variability has been observed on a rocky planet outside the solar system – and believe it could be due to huge amounts of volcanic activity, further adding to the mystery of what had been nicknamed the ‘diamond planet’.

This is the first time we’ve seen such drastic changes in light emitted from an exoplanet

Nikku Madhusudhan

NASA/JPL-Caltech/R. Hurt

Artist’s impression of super-Earth 55 Cancri e, showing a hot partially-molten surface of the planet before and after possible volcanic activity on the day side.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes