̽��ֱ�� of Cambridge - Brice-Olivier Demory

First atmospheric study of Earth-sized exoplanets using Hubble telescope

sjr81 — Wed, 20 Jul 2016 17:15:38 +0000

Embarking on the first attempt at detecting the atmospheres of planets outside our solar system, a team of Cambridge and international researchers discovered that the exoplanets TRAPPIST-1b and TRAPPIST-1c, approximately 40 light-years away, are unlikely to have puffy, hydrogen-dominated atmospheres such as those usually found on gaseous worlds like Jupiter or Saturn.

̽��ֱ��lack of a hydrogen-helium envelope increases the Earth-likeliness of these planets and has caused considerable excitement among researchers taking part in the study. ̽��ֱ��results of their findings are published today in the journal Nature.

“Humanity’s remote exploration of alien environments has truly started,” said Amaury Triaud, a research fellow at Cambridge’s Institute of Astronomy. “It is tantalizing to think that with another ten similar observations, we would start distinguishing whether those planets are more Venus-like, more Earth-like, or if they are radically different.”

Researchers observed the planets in near-infrared light and used spectroscopy to decode a change of light as the planets transited in front of their stars. During transit, starlight shines through a planet’s atmosphere making it possible to deduce its chemical makeup.

Both planets orbit TRAPPIST-1 – an ultracool dwarf star that is much cooler and redder than the sun, and barely larger than Jupiter. TRAPPIST-1 has a mass 8% that of the Sun and is located in the constellation of Aquarius. ̽��ֱ��planets orbiting the star were discovered in late 2015 through a series of observations by the TRAnsiting Planets and PlanetesImals Small Telescope (TRAPPIST), a Belgian robotic telescope located at ESO’s (European Southern Observatory’s) La Silla Observatory in Chile. ̽��ֱ��small size of the star TRAPPIST-1 boosts the signal produced by the planets’ atmospheres, easing their study by nearly 100 times compared to similar planets orbiting stars like the Sun.

TRAPPIST-1b completes a circuit around its red dwarf star in 1.5 days and TRAPPIST-1c in 2.4 days. Thanks to the faintness of the star they orbit, and to the planet’s short orbits, it is possible that parts of their surfaces have temperatures similar to the Earth. While it remains unclear whether the planets are habitable, they are the first worlds for which we can determine the existence of a habitable climate.

On May 4, astronomers took advantage of a rare simultaneous transit, when both planets crossed the face of their star within minutes of each other, to measure starlight as it filtered through any existing atmosphere. This double transit, which occurs only once every two years, provided a chance to hasten the atmospheric study of TRAPPIST-1b and TRAPPIST-1c.

̽��ֱ��researchers now hope to use Hubble to conduct follow-up observations to search for thinner atmospheres, composed of elements heavier than hydrogen, like those of Earth and Venus.

Observations from future telescopes, including NASA’s James Webb Space Telescope, will help determine the full composition of these atmospheres and hunt for potential biosignatures, such as carbon dioxide and ozone, in addition to water vapor and methane. Webb also will analyze a planet’s temperature and surface pressure – key factors in assessing its habitability.

“Our observations demonstrate that Hubble has the capacity to play a central role,” said lead researcher Julien de Wit, of the Massachusetts Institute of Technology. “It can carry-out an atmospheric pre-screening, to tell astronomers which of these Earth-sized planets are prime candidates for more detailed study with the Webb telescope.”

̽��ֱ��TRAPPIST telescope identified these two Earth-sized worlds during a prototype run for a more ambitious venture, called SPECULOOS, which is currently in construction at Cerro Paranal, Chile. SPECULOOS will monitor 1,000 nearby red dwarf stars seeking additional Earth-sized worlds.

Professor Didier Queloz, Professor of Physics at the Cavendish Laboratory, and a founding member of the project, said: “Within the next five years, SPECULOOS will likely detect 20-30 new Earth-sized planets. All of them will have atmospheres that can be investigated by the James Webb.”

Dr Brice-Olivier Demory, a senior research associate at the Cavendish Laboratory, said: “Soon we will have the right targets, and the right telescopes to start investigating rocky planet atmospheres beyond our Solar system. Finding out whether other worlds are indeed Earth-like is only a matter of time.”

̽��ֱ��Hubble Space Telescope is a project of international cooperation between NASA and ESA. Goddard manages the telescope and STScI conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington.

Two Earth-sized exoplanets have become the first rocky worlds to have their atmospheres studied using the Hubble Space Telescope.

Humanity’s remote exploration of alien environments has truly started.

Amaury Triaud

NASA

Artist's View of Planets Transiting Red Dwarf Star in TRAPPIST-1 System

̽��ֱ��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.

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Map of rocky exoplanet reveals a lava world

sc604 — Wed, 30 Mar 2016 17:00:00 +0000

An international team of astronomers, led by the ̽��ֱ�� of Cambridge, has obtained the most detailed ‘fingerprint’ of a rocky planet outside our solar system to date, and found a planet of two halves: one that is almost completely molten, and the other which is almost completely solid.

According to the researchers, conditions on the hot side of the planet are so extreme that it may have caused the atmosphere to evaporate, with the result that conditions on the two sides of the planet vary widely: temperatures on the hot side can reach 2500 degrees Celsius, while temperatures on the cool side are around 1100 degrees. ̽��ֱ��results are reported in the journal Nature.

Using data from NASA’s Spitzer Space Telescope, the researchers examined a planet known as 55 Cancri e, which orbits a sun-like star located 40 light years away in the Cancer constellation, and have mapped how conditions on the planet change throughout a complete orbit, the first time this has been accomplished for such a small planet.

55 Cancri e is a ‘super Earth’: a rocky exoplanet about twice the size and eight times the mass of Earth, and orbits its parent star so closely that a year lasts just 18 hours. ̽��ֱ��planet is also tidally locked, meaning that it always shows the same face to its parent star, similar to the Moon, so there is a permanent ‘day’ side and a ‘night’ side. Since it is among the nearest super Earths whose composition can be studied, 55 Cancri e is among the best candidates for detailed observations of surface and atmospheric conditions on rocky exoplanets.

Uncovering the characteristics of super Earths is difficult, since they are so small compared to the parent star and their contrast relative to the star is extremely small compared to larger, hotter gas giant planets, the so-called ‘hot Jupiters’.

“We haven’t yet found any other planet that is this small and orbits so close to its parent star, and is relatively close to us, so 55 Cancri e offers lots of possibilities,” said Dr Brice-Olivier Demory of the ̽��ֱ��’s Cavendish Laboratory, the paper’s lead author. “We still don’t know exactly what this planet is made of – it’s still a riddle. These results are like adding another brick to the wall, but the exact nature of this planet is still not completely understood.”

55 Cancri e has been extensively studied since it was discovered in 2011. Based on readings taken at different points in time, it was thought to be a water world, or even made of diamond, but researchers now believe that it is almost completely covered by lava.

“We have entered a new era of atmospheric remote sensing of rocky exoplanets,” said study co-author Dr Nikku Madhusudhan, from the Institute of Astronomy at Cambridge. “It is incredible that we are now able to measure the large scale temperature distribution on the surface of a rocky exoplanet.”

Based on these new infrared measurements, the ‘day’ side of the planet appears to be almost completely molten, while the ‘night’ side is almost completely solid. ̽��ֱ��heat from the day side is not efficiently circulated to the night side, however. On Earth, the atmosphere aids in the recirculation of heat, keeping the temperature across the whole planet within a relatively narrow range. But on 55 Cancri e, the hot side stays hot, and the cold side stays cold.

According to Demory, one possibility for this variation could be either a complete lack of atmosphere, or one which has been partially destroyed due to the strong irradiation from the nearby host star. “On the day side, the temperature is around 2500 degrees Celsius, while on the night side it’s about 1100 degrees – that’s a huge difference,” he said. “We think that there could still be an atmosphere on the night side, but temperatures on the day side are so extreme that the atmosphere may have evaporated completely, meaning that heat is not being efficiently transferred, or transferred at all from the day side to the night side.”

Another possibility for the huge discrepancy between the day side and the night side may be that the molten lava on the day side moves heat along the surface, but since lava is mostly solid on the night side, heat is not moved around as efficiently.

What is unclear however, is where exactly the ‘extra’ heat on 55 Cancri e comes from in the first place, since the observations reveal an unknown source of heat that makes the planet hotter than expected solely from the irradiation from the star – but the researchers may have to wait until the next generation of space telescopes are launched to find out.

For Demory, these new readings also show just how difficult it will be to detect a planet that is similar to Earth. ̽��ֱ��smaller a planet is, the more difficult it is to detect. And once a rocky planet has been found, there is the question of whether it lies in the so-called habitable zone, where life can be supported. “ ̽��ֱ��problem is, people don’t agree on what the habitable zone is,” said Demory. “For example, some studies consider Mars and Venus to be in the habitable zone, but life as we know it is not possible on either of those planets. Understanding the surface and climate properties of these other worlds will eventually allow us to put the Earth’s climate and habitability into context.”

One possibility might be to look at stars which are much cooler and smaller than our sun, such as the M-dwarfs, which would mean that planets could be much closer to their star and still be in the habitable zone. ̽��ֱ��sizes of such planets relative to their star would be larger, which make them more detectable from Earth.

But for the time being, Demory and his colleagues plan to keep studying 55 Cancri e, in order to see what other secrets it might hold, including the possibility that it might be surrounded by a torus of gas and dust, which could account for some of the variations in the data. And in 2018, the successor to Hubble and Spitzer, the James Webb Space Telescope, will launch, allowing astronomers to look at planets outside our solar system with entirely new levels of precision.

Reference:
Brice-Olivier Demory et al. ‘A map of the extreme day-night temperature gradient of a super-Earth exoplanet.’ Nature (2016). DOI: 10.1038/nature17169

̽��ֱ��most detailed map of a small, rocky ‘super Earth’ to date reveals a planet almost completely covered by lava, with a molten ‘hot’ side and solid ‘cool’ side.

We still don’t know exactly what this planet is made of – it’s still a riddle. These results are like adding another brick to the wall, but the exact nature of this planet is still not completely understood.

Brice-Olivier Demory

55 Cancri e

NASA/JPL-Caltech/R. Hurt

Illustration of the hot lava world 55 Cancri e

̽��ֱ��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.

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