Institute of Astronomy

Astronomy News

First atmospheric study of Earth-sized exoplanets excites researchers

21 July 2016 - 11:41am

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.  

The 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. The 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. The 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. The 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.

The 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.”

The 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.”

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

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Vast asteroid created 'Man in Moon's eye' crater

21 July 2016 - 11:38am

One of the biggest craters on the Moon's surface was created by an asteroid more than 250km across, a study suggests.

Planet Nine may have tilted entire solar system except the sun

20 July 2016 - 8:47am

The sun's spin isn't totally upright compared with the orbits of the planets. Could this be because a jealous, distant world shoved its siblings?

What lies beneath: Venus' surface revealed through the clouds

19 July 2016 - 9:07am

Using observations from ESA's Venus Express satellite, scientists have shown for the first time how weather patterns seen in Venus' thick cloud layers are directly linked to the topography of the surface below. Rather than acting as a barrier to our observations, Venus' clouds may offer insight into what lies beneath.

Einstein’s clock: The doomed black hole to set your watch by

19 July 2016 - 9:05am

Every 12 years, a black hole at the centre of a distant galaxy completes an orbit around an even bigger black hole, marking this with a violent outburst

Baby stars grow big and strong by eating their own burst bubbles

18 July 2016 - 9:14am

A new simulation suggests the most massive stars in the universe got so big by taking advantage of the same physics that makes mushroom clouds

Mysterious swoosh caused by pulsars hugging companions close

18 July 2016 - 9:12am

A pair of dead stars give off bizarre radio signals, which could be the calling card of ultra-dense companions orbiting them at near the speed of light

Five incredible things we know about Pluto since 2015’s fly-by

15 July 2016 - 9:19am

New Horizons buzzed by Pluto and its moons last July, giving us a front-row seat to see icy peaks, towering atmospheric haze, a kilometres-deep canyon and more

Largest-ever map of 1.2 million galaxies measures dark energy

15 July 2016 - 9:14am

A decade-long survey of galaxies in the universe has revealed the crispest measurements yet of how dark energy drives the expansion fo the universe

Imaging the water snow-line during a protostellar outburst

14 July 2016 - 9:16am

Imaging the water snow-line during a protostellar outburst

Nature 535, 7611 (2016). doi:10.1038/nature18612

Authors: Lucas A. Cieza, Simon Casassus, John Tobin, Steven P. Bos, Jonathan P. Williams, Sebastian Perez, Zhaohuan Zhu, Claudio Caceres, Hector Canovas, Michael M. Dunham, Antonio Hales, Jose L. Prieto, David A. Principe, Matthias R. Schreiber, Dary Ruiz-Rodriguez & Alice Zurlo

A snow-line is the region of a protoplanetary disk at which a major volatile, such as water or carbon monoxide, reaches its condensation temperature. Snow-lines play a crucial role in disk evolution by promoting the rapid growth of ice-covered grains. Signatures of the carbon monoxide snow-line (at temperatures of around 20 kelvin) have recently been imaged in the disks surrounding the pre-main-sequence stars TW Hydra and HD163296 (refs 3, 10), at distances of about 30 astronomical units (au) from the star. But the water snow-line of a protoplanetary disk (at temperatures of more than 100 kelvin) has not hitherto been seen, as it generally lies very close to the star (less than 5 au away for solar-type stars). Water-ice is important because it regulates the efficiency of dust and planetesimal coagulation, and the formation of comets, ice giants and the cores of gas giants. Here we report images at 0.03-arcsec resolution (12 au) of the protoplanetary disk around V883 Ori, a protostar of 1.3 solar masses that is undergoing an outburst in luminosity arising from a temporary increase in the accretion rate. We find an intensity break corresponding to an abrupt change in the optical depth at about 42 au, where the elevated disk temperature approaches the condensation point of water, from which we conclude that the outburst has moved the water snow-line. The spectral behaviour across the snow-line confirms recent model predictions: dust fragmentation and the inhibition of grain growth at higher temperatures results in soaring grain number densities and optical depths. As most planetary systems are expected to experience outbursts caused by accretion during their formation, our results imply that highly dynamical water snow-lines must be considered when developing models of disk evolution and planet formation.

Astrophysics: Variable snow lines affect planet formation

14 July 2016 - 9:16am

Astrophysics: Variable snow lines affect planet formation

Nature 535, 7611 (2016). doi:10.1038/535237a

Authors: Brenda Matthews

Observations of the disk of dust and gas around a nascent star reveal that the distance from the star at which water in the disk forms ice is variable. This variation might hinder the formation of planets. See Letter p.258

Chemistry: Cosmic rays breed organics in space

14 July 2016 - 9:14am

Chemistry: Cosmic rays breed organics in space

Nature 535, 7611 (2016). doi:10.1038/535203b

Cosmic rays help to form the Universe's complex organic molecules — the building blocks of life on Earth.The interstellar gas clouds that give birth to stars and planets are rich in organic molecules, but scientists have struggled to explain how these formed. A team

Planetary science: Triple star hosts stable planet

14 July 2016 - 9:14am

Planetary science: Triple star hosts stable planet

Nature 535, 7611 (2016). doi:10.1038/535202a

An extrasolar planet in an exotic triple-star system lives in surprising harmony with the three suns hanging in its sky.Kevin Wagner of the University of Arizona in Tucson and his colleagues used the European Southern Observatory's Very Large Telescope in Chile to study the

Stellar Outburst Brings Water Snow Line Into View

14 July 2016 - 9:11am
The Atacama Large Millimeter/submillimeter Array (ALMA) has made the first ever resolved observation of a water snow line within a protoplanetary disc. This line marks where the temperature in the disc surrounding a young star drops sufficiently low for snow to form. A dramatic increase in the brightness of the young star V883 Orionis flash heated the inner portion of the disc, pushing the water snow line out to a far greater distance than is normal for a protostar, and making it possible to observe it for the first time. The results are published in the journal Nature on 14 July 2016.

Baby star illuminates icy wall between rocky planets and giants

14 July 2016 - 9:11am

A newborn star's fiery temper tantrum pushed its "snow line" far enough out that astronomers could spot it

Milky Way’s bulge may have been formed by the galaxy buckling

14 July 2016 - 9:10am

The origin of the bump at the centre of many disc galaxies has long puzzled astronomers, but now there’s evidence it could be due to a cosmic kink

Gravitational vortex provides new way to study matter close to a black hole

13 July 2016 - 9:39am

ESA's orbiting X-ray observatory, XMM-Newton, has proved the existence of a 'gravitational vortex' around a black hole. The discovery, aided by NASA's NuSTAR mission, solves a mystery that has eluded astronomers for more than 30 years and will allow them to map the behaviour of matter very close to black holes. It could also open the door to future investigations of Albert Einstein's general relativity.

Deepest Ever Look into Orion

13 July 2016 - 9:38am
ESO’s HAWK-I infrared instrument on the Very Large Telescope (VLT) in Chile has been used to peer deeper into the heart of Orion Nebula than ever before. The spectacular picture reveals about ten times as many brown dwarfs and isolated planetary-mass objects than were previously known. This discovery poses challenges for the widely accepted scenario for Orion’s star formation history.

Gravitational vortex provides new way to study matter close to a black hole

13 July 2016 - 9:15am

Matter falling into a black hole heats up as it plunges to its doom. Before it passes into the black hole and is lost from view forever, it can reach millions of degrees. At that temperature it shines x-rays into space.

In the 1980s, astronomers discovered that the x-rays coming from black holes vary on a range of timescales and can even follow a repeating pattern with a dimming and re-brightening taking 10 seconds to complete. As the days, weeks and then months progress, the pattern’s period shortens until the oscillation takes place 10 times every second. Then it suddenly stops altogether.

This phenomenon was dubbed a Quasi Periodic Oscillation (QPO). During the 1990s, astronomers began to suspect that the QPO was associated with a gravitational effect predicted by Einstein’s general relativity which suggested that a spinning object will create a kind of gravitational vortex. The effect is similar to twisting a spoon in honey: anything embedded in the honey will be ‘dragged’ around by the twisting spoon. In reality, this means that anything orbiting around a spinning object will have its motion affected. If an object is orbiting at an angle, its orbit will ‘precess’ – in other words, the whole orbit will change orientation around the central object. The time for the orbit to return to its initial condition is known as a precession cycle.

In 2004, NASA launched Gravity Probe B to measure this so-called Lense-Thirring effect around Earth. By analysing the resulting data, scientists confirmed that the spacecraft would turn through a complete precession cycle once every 33 million years. Around a black hole, however, the effect would be much stronger because of the stronger gravitational field: the precession cycle would take just a matter of seconds to complete, close to the periods of the QPOs.

An international team of researchers, including Dr Matt Middleton from the Institute of Astronomy at the University of Cambridge, has used the European Space Agency’s XMM-Newton and NASA’s NuSTAR, both x-ray observatories, to study the effect of black hole H1743-322 on a surrounding flat disc of matter known as an ‘accretion disk’.

Close to a black hole, the accretion disc puffs up into a hot plasma, a state of matter in which electrons are stripped from their host atoms – the precession of this puffed up disc has been suspected to drive the QPO. This can also explain why the period changes - the place where the disc puffs up gets closer to the black hole over weeks and months, and, as it gets closer to the black hole, the faster its Lense-Thirring precession becomes.

The plasma releases high energy radiation that strikes the matter in the surrounding accretion disc, making the iron atoms in the disc shine like a fluorescent light tube. Instead of visible light, the iron releases X-rays of a single wavelength – referred to as ‘a line’. Because the accretion disc is rotating, the iron line has its wavelength distorted by the Doppler effect: line emission from the approaching side of the disc is squashed – blue shifted – and line emission from the receding disc material is stretched – red shifted. If the plasma really is precessing, it will sometimes shine on the approaching disc material and sometimes on the receding material, making the line wobble back and forth over the course of a precession cycle.

It is this ‘wobble’ that has been observed by the researchers.

“Just as general relativity predicts, we’ve seen the iron line wobble as the accretion disk orbits the black hole,” says Dr Middleton. “This is what we’d expect from matter moving in a strong gravitational field such as that produced by a black hole.”

This is the first time that the Lense-Thirring effect has been measured in a strong gravitational field. The technique will allow astronomers to map matter in the inner regions of accretion discs around back holes. It also hints at a powerful new tool with which to test general relativity. Einstein’s theory is largely untested in such strong gravitational fields. If astronomers can understand the physics of the matter that is flowing into the black hole, they can use it to test the predictions of general relativity as never before - but only if the movement of the matter in the accretion disc can be completely understood.

“We need to test Einstein’s general theory of relativity to breaking point,” adds Dr Adam Ingram, the lead author at the University of Amsterdam. “That’s the only way that we can tell whether it is correct or, as many physicists suspect, an approximation – albeit an extremely accurate one.”

Larger X-ray telescopes in the future could help in the search because they could collect the X-rays faster. This would allow astronomers to investigate the QPO phenomenon in more detail. But for now, astronomers can be content with having seen Einstein’s gravity at play around a black hole.

Adapted from a press release by the European Space Agency.

Image: ESA/ATG medialab.

An international team of astronomers has proved the existence of a ‘gravitational vortex’ around a black hole, solving a mystery that has eluded astronomers for more than 30 years. The discovery will allow astronomers to map the behaviour of matter very close to black holes. It could also open the door to future investigation of Albert Einstein’s general relativity.

We need to test Einstein’s general theory of relativity to breaking pointAdam Ingram, University of AmsterdamESA/ATG medialabIllustration of gravitational vortex

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Juno probe returns first in-orbit Jupiter photo

13 July 2016 - 9:14am

The American space agency's new Juno mission to Jupiter returns its first imagery since going into orbit around the gas giant last week.