New Super-Earth Detected Within the Habitable Zone of a Nearby Cool Star

New Super-Earth Detected Within the Habitable Zone of a Nearby Cool Star

  10:12:00 AM    Science Lover

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An international team of scientists led by Carnegie's Guillem Anglada-Escudé and Paul Butler has discovered a potentially habitable super-Earth orbiting a nearby star. The star is a member of a triple star system and has a different makeup than our Sun, being relatively lacking in metallic elements. This discovery demonstrates that habitable planets could form in a greater variety of environments than previously believed.

An artistic conception of the two planets reported on in this
paper: b and c. Planet c is the one that lies in the habitable
zone of the star. Planet b is too hot to be habitable. (Credit:
Images courtesy of Guillem Anglada-Escud)

Their work will be published in The Astrophysical Journal Letters.

The team used public data from the European Southern Observatory and analyzed it with a novel data analysis method. They also incorporated new measurements from the Keck Observatory's High Resolution Echelle Spectrograph and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope.

Their planet-finding technique involved measuring the small wobbles in a star's orbit in response to a planet's gravity. Anglada-Escudé and his team focused on an M-class dwarf star called GJ 667C, which is 22 light years away. It is a member of a triple-star system. The other two stars (GJ 667AB) are a pair of orange K dwarfs, with a concentration of heavy elements only 25% that of our Sun's. Such elements are the building blocks of terrestrial planets so it was thought to be unusual for metal-depleted star systems to have an abundance of low mass planets.

GJ 667C had previously been observed to have a super-Earth (GJ 667Cb) with a period of 7.2 days, although this finding was never published. This orbit is too tight, and thus hot, to support life. The new study started with the aim of obtaining the orbital parameters of this super-Earth.

But in addition to this first candidate, the research team found the clear signal of a new planet (GJ 667Cc) with an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth. The new planet receives 90% of the light that Earth receives. However, because most of its incoming light is in the infrared, a higher percentage of this incoming energy should be absorbed by the planet. When both these effects are taken into account, the planet is expected to absorb about the same amount of energy from its star that Earth absorbs from the Sun. This would allow surface temperatures similar to Earth and perhaps liquid water, but this extreme cannot be confirmed without further information on the planet's atmosphere.

"This planet is the new best candidate to support liquid water and, perhaps, life as we know it," Anglada-Escudé said.

The team notes that the system might also contain a gas-giant planet and an additional super-Earth with an orbital period of 75 days. However, further observations are needed to confirm these two possibilities. "With the advent of a new generation of instruments, researchers will be able to survey many M dwarf stars for similar planets and eventually look for spectroscopic signatures of life in one of these worlds."

Anglada-Escudé was with Carnegie when he conducted the research, but has since moved on to University of Gottingen. His co-authors are Carnegie's Butler, Jeffrey D. Crane, Stephen A. Shectman, and Ian B. Thompson; Pamela Arriagada and Dante Minniti of Pontificia Universidad Catolica de Chile; Steve Vogt and Eugenio J. Rivera of University of California's Lick Observatory; Nader Haghighipour of the Institute for Astronomy & NASA Astrobiology Institute at University of Hawaii-Monoa; Brad D. Carter of University of Southern Queensland; C. G. Tinney, Robert A. Wittenmyer, and Jeremy A. Bailey of the University of New South Wales; Simon J. O'Toole of the Australian Astronomical Observatory; Hugh R.A. Jones of the University of Hertfordshire; and James S. Jenkins of the Universidad de Chile, Camino El Observatorio.

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The history of the universe – in 3D!

The history of the universe – in 3D!

  12:54:00 AM    Science Lover

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In an international project, astronomers have obtained exceptional 3D images of distant galaxies, seen when the Universe was half its current age. And by looking at this unique “history book” of the universe, at an epoch when the Sun and the Earth did not even exist, scientists hope to solve the puzzle of how galaxies formed in the remote past.

The team – consisting of scientists from the US’ NASA, the European Space Agency and the European Southern Observatory – obtained the images by combining the Hubble Space Telescope’s acute eye with the capacity of the Very Large Telescope (VLT) to probe the motions of gas in tiny objects.

“Hubble and VLT are real ‘time machines’ for probing the universe’s history,” said Sébastien Peirani, lead author of one of the papers reporting on this study.

DOUBLING UP

For decades, distant galaxies that emitted their light six to eight billion years ago – over half the age of the universe – were no more than small specks of light on the sky.

With the launch of the Hubble Space Telescope in the early 1990s, astronomers were able to scrutinise the structure of these galaxies in some detail for the first time.

Now, researchers are using the Hubble’s capabilities in conjunction with those of the VLT – an array of four separate optical telescopes, situated at the Paranal Observatory in northern Chile. Its Fibre Large Array Multi Element Spectrograph (FLAMES) can observe up to 130 targets at a time, which enabled the team to measure the velocity of the gas in the distant galaxies.

“By seeing how the gas is moving, it provides us with a 3D view of galaxies halfway across the universe,” said François Hammer, who led the project.

The team is now reconstituting the history of about 100 remote galaxies. The project has already provided useful insights for three such galaxies.

UNRAVELLING GALACTIC SECRETS

In one galaxy, FLAMES revealed a region full of ionised gas – hot gas composed of atoms that have been stripped of one or several electrons. This is normally due to the presence of very hot, young stars.

However, even after staring at the region for more than 11 days, Hubble did not detect any stars! “Clearly, this unusual galaxy has some hidden secrets,” researcher Mathieu Puech said.

Computer simulations suggested that the explanation lies in the collision of two very gas-rich spiral galaxies. The heat produced by the collision would ionise the gas, making it too hot for stars to form.

Another galaxy that the scientists studied showed the opposite effect. There, they discovered a bluish central region enshrouded in a reddish disc, almost completely hidden by dust.

“The models indicate that gas and stars could be spiralling inwards rapidly,” said Hammer. “This might be the first example of a disc rebuilt after a major merger.”

Finally, in a third galaxy, the team saw a rare sight: an extremely blue, elongated structure – a bar, in fact – composed of young, massive stars. Comparisons with computer simulations showed that the properties of this object are well reproduced by a collision between two galaxies of unequal mass.

“The combination of Hubble and the VLT, along with modern computer simulations, allows us to model distant galaxies almost as nicely as the close ones,” Hammer said.

The team is now extending its analyses to the whole sample of galaxies observed.

“The next step will then be to compare this with closer galaxies, and so, piece together a picture of the evolution of galaxies over half the age of the universe,” he concluded.

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