Life may be harder to identify on some exoplanets

Oct 11, 2013

Finding life on exoplanets may be more difficult than people thought, said Feng Tian, a professor at the Center for Earth System Science at Tsinghua University in Beijing, China. The report was presented last week to the American Astronomical Society Division for Planetary Sciences meeting in Denver, CO. The result is of special interest because it may shed light on how and where life could be identified on exoplanets.

Current efforts to find exoplanets with the potential to harbor (habitable planets) and exoplanets with life (inhabited planets) focus on smaller stars than the Sun, because these so called M dwarfs or make up more than 75% of stars in the solar neighborhood. Therefore it may be possible to find habitable planets around these small stars with the current level of technology. Thus searching for habitable planets around M dwarfs is considered the fast track to find a second Earth. High levels of atmospheric oxygen are considered the most promising indicator for life on exoplanets.

However recent observations, using the Hubble Space Telescope, of several planet-hosting M dwarfs show that the ultraviolet (UV) properties of these small stars are quite different from those of the Sun (France et al. 2013). Using the observed UV spectrum of the M dwarf star GJ 876, Feng Tian and his US and Argentina colleagues (Kevin France and Jeffrey Linsky from University of Colorado at Boulder, Pablo J. D. Mauas and Mariela C. Vieytes from the Instituto de Astronomia y Fisica del Espacio, Buenos Aires, Argentina) have shown (Tian et al. 2013) that the atmospheres of a hypothetical around GJ 876 could build up significant levels of oxygen even in the absence of life. "In this case the atmosphere of a lifeless planet can be close to that of the Earth's 2.2 billion years ago, after the so called Great Oxidation Event in Earth's geological history," said Feng Tian.

In today's report, Feng Tian and his colleagues further studied Earth-mass planets using the UV spectra of 4 other M dwarfs, including GJ 667C which contains 3 potentially habitable planets. These studies provided further support to their previous claim: "Before we can claim the discovery of life on , we have to examine the stars harboring these planets more carefully."

"Prof. Feng Tian's research addresses one of the most important questions of contemporary astrophysics and indeed of great interest to the general public: Are there other habitable planets near Earth, and is there any evidence that they are indeed inhabited?" commented Professor Jeffrey Linsky of the University of Colorado at Boulder.

"The authors of this paper make an important point regarding the confidence we could have in the detection of O2 simultaneously with H2O and CO2, as a biosignature in the spectrum of an Earth-like exoplanet around an M star," commented Dr. Alain Leger of the Institut d'Astrophysique Spatiale at Université Paris XI, France.

Like all new findings, the work requires further confirmation by other scientists. Dr. Leger said: "This is somewhat sending the cat among the pigeons in our confidence in the O2, H2O, and CO2 biosignature, but in a limited way. It concerns only M stars and the presence of O2 in small amounts."

"The effects of stellar flares on the atmosphere of the hypothetical Earth-like planet around GJ 876 have not been considered in this work.... At this point, we do not have a sufficient understanding of the amplitude and frequency of such flares on older, low-mass exoplanet host stars to make predictions about their impact on the production of biomarker signatures," said Dr. Kevin France, a coauthor of the work from the University of Colorado at Boulder.

Although the observed M dwarfs all present UV properties quite different from the Sun, more can be learned by longer exposures on more with the potential to harbor habitable planets.

Explore further: Gas cloud in the galactic centre is part of a larger gas streamer

Provided by Tsinghua University

3.7 /5 (6 votes)
add to favorites email to friend print save as pdf

Related Stories

How common are earths around small stars?

Jun 03, 2013

(Phys.org) —The Kepler mission has revolutionized the study of exoplanet statistics by increasing the number of known extrasolar planets and planet candidates by a factor of five, and by discovering systems ...

A hot potential habitable exoplanet around Gliese 163

Aug 31, 2012

A new superterran exoplanet (aka Super-Earth) was found in the stellar habitable zone of the red dwarf star Gliese 163 by the European HARPS team. The planet, Gliese 163c, has a minimum mass of 6.9 Earth ...

Red dwarf stars could strip away planetary protection

Jul 02, 2013

(Phys.org) —Red dwarf stars are the commonest type of stars, making up about 75% of the stars in our Galaxy. They are much smaller and much less massive than our Sun and for that reason a lot dimmer. If ...

Recommended for you

Image: Hubble captures the Egg Nebula

6 hours ago

This colourful image shows a cosmic lighthouse known as the Egg Nebula, which lies around 3000 light-years from Earth. The image, taken with the NASA/ESA Hubble Space Telescope, has captured a brief but dramatic ...

'Blockbuster' science images

Nov 21, 2014

At this point, the blockbuster movie Interstellar has created such a stir that one would almost have to be inside a black hole not to know about it. And while the science fiction thriller may have taken some ...

Estimating the magnetic field of an exoplanet

Nov 20, 2014

Scientists developed a new method which allows to estimate the magnetic field of a distant exoplanet, i.e., a planet, which is located outside the Solar system and orbits a different star. Moreover, they ...

It's filamentary: How galaxies evolve in the cosmic web

Nov 20, 2014

How do galaxies like our Milky Way form, and just how do they evolve? Are galaxies affected by their surrounding environment? An international team of researchers, led by astronomers at the University of ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.