Institute of Astronomy

Astronomy News

Astronomy: A small star with an Earth-like planet

12 November 2015 - 9:29am

Astronomy: A small star with an Earth-like planet

Nature 527, 7577 (2015). doi:10.1038/527169a

Authors: Drake Deming

A rocky planet close in size to Earth has been discovered in the cosmic vicinity of our Sun. The small size and proximity of the associated star bode well for studies of the planet's atmosphere. See Letter p.204

A rocky planet transiting a nearby low-mass star

12 November 2015 - 9:29am

A rocky planet transiting a nearby low-mass star

Nature 527, 7577 (2015). doi:10.1038/nature15762

Authors: Zachory K. Berta-Thompson, Jonathan Irwin, David Charbonneau, Elisabeth R. Newton, Jason A. Dittmann, Nicola Astudillo-Defru, Xavier Bonfils, Michaël Gillon, Emmanuël Jehin, Antony A. Stark, Brian Stalder, Francois Bouchy, Xavier Delfosse, Thierry Forveille, Christophe Lovis, Michel Mayor, Vasco Neves, Francesco Pepe, Nuno C. Santos, Stéphane Udry & Anaël Wünsche

M-dwarf stars—hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun—are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.

Planetary science: How Mars loses its atmosphere

12 November 2015 - 9:26am

Planetary science: How Mars loses its atmosphere

Nature 527, 7577 (2015). doi:10.1038/527136a

Solar storms have blasted much of Mars's tenuous atmosphere into space over billions of years, making the planet the barren world it is today.A series of papers has outlined the first results from NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, which has been

Ancient stars at the centre of the Milky Way contain ‘fingerprints’ from the very early Universe

12 November 2015 - 9:24am

An international team of astronomers, led researchers from the University of Cambridge and the Australian National University, have identified some of the oldest stars in our galaxy, which could contain vital clues about the early Universe, including an indication of how the first stars died.

These stars, which have been at the very centre of the Milky Way for billions of years, contain extremely low amounts of metal: one of the stars is the most metal-poor star yet discovered in the centre of our galaxy. These stars also contain chemical fingerprints which indicate that the very first stars may have died in spectacular deaths known as hypernovae, which were ten times more energetic than a regular supernova. The findings, reported today (11 November) in the journal Nature, could aid in understanding just how much the Universe has changed over the past 13.7 billion years.

For decades, astronomers have been trying to determine what the Universe was like soon after the Big Bang – understanding how the first stars and galaxies formed is crucial to this goal. While some astronomers are looking outward to galaxies billions of light years away to untangle this mystery, others are looking inward to the centre of our galaxy.

If you’ve ever looked up at the night sky from a dark place you might see the centre of the Milky Way. There are billions of stars in our galaxy, and astronomers are interested in picking out the oldest stars and finding out about their chemical composition and movements.

Soon after the Big Bang, the Universe was entirely made up of only hydrogen, helium and small amounts of lithium. All of the other elements, like the oxygen we breathe or the sodium in our toothpaste, have been made inside stars or when they die as supernovae. This has led astronomers to search for extremely metal-poor stars: stars with lots of hydrogen, but very little of any other element.

It had been thought that the very first stars formed in the centre of the galaxy, where the effects of gravity are strongest. But after decades of searches, astronomers found that most stars in the centre of our galaxy have a similar metal content of those much closer to us. While the stars at the centre of the galaxy are about seven billion years older than the Sun, they’re still not old enough to understand what the conditions were like in the early Universe.

Using telescopes in Australia and Chile, astronomers may have landed on a winning strategy to find the oldest stars in the galaxy. Stars with a low metal content look slightly bluer than other stars: a key difference that can be used to sift through the millions of stars at the centre of the Milky Way.

Using images taken with the ANU SkyMapper telescope in Australia, the team selected 14,000 promising stars to look at in more detail, with a spectrograph on a bigger telescope. A spectrograph breaks up the light of the star, much like a prism, allowing astronomers to make detailed measurements.

Their best 23 candidates were all very metal-poor, leading the researchers to a larger telescope in the Atacama desert in Chile. From this data the team identified nine stars with a metal content less than one-thousandth of the amount seen in the Sun, including one with one-ten-thousandth the amount – now the record breaker for the most metal-poor star in the centre of the galaxy.

“If you could compress all the iron in the Sun to the size of your fist, some of these stars would contain just a tiny pebble by comparison,” said Dr Andrew Casey of Cambridge’s Institute of Astronomy, one of the study’s co-authors. “They’re very, very different kinds of stars.”

However, knowing that these stars have low amounts of metal wasn’t enough to be certain that they formed very early in the Universe. They could be stars that formed much later in other parts of the galaxy that weren’t as dense, and they are just now passing through the centre. To separate those possibilities, researchers measured distances and used precise measurements of the stars’ movement in the sky to predict how the stars were moving, and where they had been in the past.

They found that while some stars were just passing through, seven of the stars had spent their entire lives in the very centre of our galaxy. Computer simulations suggest that stars like this must have formed in the very early Universe.

“There are so many stars in the centre of our Galaxy – finding these rare stars is really like looking for a needle in a haystack,” said Casey. “But if we select these stars in the right way, it’s like burning down the farm and sweeping up the needles with a magnet.”

When the very first stars in the galaxy died, they left a chemical signature on the generation of stars reported on in this latest study. This chemical fingerprint suggests the very first stars may have died in spectacular deaths known as hypernovae, an explosion ten times more energetic than a regular supernova. This would make it one of the most energetic things in the Universe, and very different from the kinds of stellar explosions we see today.

“This work confirms that there are ancient stars in the centre of our Galaxy. The chemical signature imprinted on those stars tells us about an epoch in the Universe that’s otherwise completely inaccessible,” said Casey. “The Universe was probably very different early on, but to know by how much, we’ve really just got to find more of these stars: more needles in bigger haystacks.”

L.M. Howes et. al. ‘Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way.’ Nature (2015). DOI: 10.1038/nature15747

Astronomers have discovered some of the oldest stars in the galaxy, whose chemical composition and movements could tell us what the Universe was like soon after the Big Bang.

Finding these rare stars is really like looking for a needle in a haystack. But if we select these stars in the right way, it’s like burning down the farm and sweeping up the needles with a magnetAndrew CaseyESOAn artist's impression of a hypernova, an explosive death of a star roughly ten times more energetic than a normal supernova.

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


Far-off Solar System object spied

12 November 2015 - 9:12am

Astronomers have identified the most distant object yet in the Solar System - a likely icy body three times further away than even far-flung Pluto.

Super-scope project breaks ground

12 November 2015 - 9:11am

A ceremony is held to mark the start of construction of one of the key astronomical facilities of the next decade - the Giant Magellan Telescope.

'Venus twin' excites astronomers

12 November 2015 - 9:08am

Astronomers hunting distant worlds say they have made one of their most significant discoveries to date - what could be a kind of hot twin to our Venus.

Most distant solar system object yet could hint at hidden planet

11 November 2015 - 9:05am

A newly discovered rocky body is more than three times more distant than Pluto. It and its companions could help solve a mystery about the outer solar system

Pluto surprises with ice volcanoes and alien weather

10 November 2015 - 9:32am

New revelations from NASA's New Horizons probe shows Pluto's diverse geology is blanketed with a more compact atmosphere than we thought

Four Months after Pluto Flyby, NASA’s New Horizons Yields Wealth of Discovery

10 November 2015 - 9:19am
From possible ice volcanoes to twirling moons, NASA’s New Horizons science team is discussing more than 50 exciting discoveries about Pluto at this week’s 47th Annual Meeting of the American Astronomical Society’s Division for Planetary Sciences in National Harbor, Maryland.

Pluto may have ice volcanoes

10 November 2015 - 9:17am

Two possible cryo-volcanoes are identified on the surface of Pluto - huge mountains with a hole in the top that may spew a slurry of ices.

'Twice-baked' model for Moon origin

10 November 2015 - 9:17am

A new model of the Moon's formation suggests it developed in two stages, leading to inner and outer layers with different compositions.

Hot Jupiters may have formed through planetary billiards

9 November 2015 - 9:55am

The first exoplanets found were gas giants orbiting close to their stars – a study suggests they could be built from collisions of several smaller planets

Shining a light on the aurora of Mars

6 November 2015 - 10:51am

ESA's Mars Express has shed new light on the Red Planet's rare ultraviolet aurora by combining for the first time remote observations with in situ measurements of electrons hitting the atmosphere.

Deserts and dunes: Earth as an analogue for Titan

6 November 2015 - 10:51am

By comparing radar images of areas on Titan to those of Earth's deserts, scientists have identified two distinct types of sand dune on Saturn's largest moon – and discovered eroded structures that indicate that Titan's climate may have once been very different.

Gaia's sensors scan a lunar transit

6 November 2015 - 10:51am

Located 1.5 million km from the Earth, ESA's Gaia spacecraft is scanning the sky to conduct the most detailed census of stars in our Galaxy. However, on 6 November, it will be perfectly placed to witness a rare event that will involve objects much closer to home – a lunar transit across the Sun.

Salt flats on Europa mean moon’s ocean may come to surface

6 November 2015 - 10:50am

Jupiter's icy moon is a favourite of alien-hunters, thanks to its buried ocean. Now it seems the ocean could come to the surface - and it might be life friendly

Bright light may not be dark matter’s smoking gun after all

6 November 2015 - 10:50am

Dwarf galaxy observations dash astronomers' hopes that the signal at the centre of the Milky Way was caused by dark matter particles colliding

NASA probe shows how solar burps may have stripped Mars of water

6 November 2015 - 10:49am

The MAVEN orbiter is trying to figure out why the Red Planet lost all its water – and a massive solar flare in March could help

Historic Rosetta mission to end with crash into comet

6 November 2015 - 10:46am

Historic Rosetta mission to end with crash into comet

Nature 527, 7576 (2015).

Author: Elizabeth Gibney

There were other options, but super close-up shots on descent will provide science bonanza.