Earth-like planets orbiting other stars in the Milky Way are three times more likely to have the same type of minerals as Earth than astronomers had previously thought. In fact, conditions for making the building blocks of Earth-like rocks are ubiquitous throughout the Milky Way. The results of a new study of the chemical evolution of our galaxy are being presented today by Prof Brad Gibson, of the University of Hull, at the National Astronomy Meeting in Llandudno.
Minerals made from building blocks of carbon, oxygen, magnesium, and
silicon are thought to control the landscape of rocky planets that form
in solar systems around Sun-like stars. A subtle difference in
mineralogy can have a big effect on plate tectonics, heating and cooling
of the planet’s surface, all of which can affect whether a planet is
ultimately habitable. Until now, astronomers thought that rocky planets
fell into three distinct groups: those with a similar set of building
blocks to Earth, those that had a much richer concentration of carbon,
and those that had significantly more silicon than magnesium.
“The ratio of elements on Earth has led to the chemical conditions
‘just right’ for life. Too much magnesium or too little silicon and your
planet ends up having the wrong balance between minerals to form the
type of rocks that make up the Earth’s crust,” said Gibson. “Too much
carbon and your rocky planet might turn out to be more like the graphite
in your pencil than the surface of a planet like the Earth.”
Gibson and team from the E.A. Milne Centre for Astrophysics at the
University of Hull have constructed a sophisticated simulation of the
chemical evolution of the Milky Way, which results in an accurate
recreation of the Milky Way as we see it today. This has allowed them to
zoom in and examine the chemistry of processes, such as planetary
formation, in detail. Their findings came as something of a surprise.
“At first, I thought we’d got the model wrong!” explained Gibson. “As
an overall representation of the Milky Way, everything was pretty much
perfect. Everything was in the right place; the rates of stars forming
and stars dying, individual elements and isotopes all matched
observations of what the Milky Way is really like.
But when we looked at
planetary formation, every solar system we looked at had the same
elemental building blocks as Earth, and not just one in three. We
couldn’t find a fault with the model, so we went back and checked the
observations. There we found some uncertainties that were causing the
one-in-three result. Removing these, observations agreed with our
predictions that the same elemental building blocks are found in every
exoplanet system, wherever it is in the galaxy.”
The cloud out of which the solar system formed has approximately
twice as many atoms of oxygen as carbon, and roughly five atoms of
silicon for every six of magnesium. Observers trying to ascertain the
chemical make-up of planetary systems have tended to look at large
planets orbiting very bright stars, which can lead to uncertainties of
10 or 20 per cent. In addition, historically the spectra of oxygen and
nickel have been hard to differentiate. Improvements in spectroscopy
techniques have cleaned up the oxygen spectra, providing data that
matches the Hull team’s estimates.
“Even with the right chemical building blocks, not every planet will
be just like Earth, and conditions allowing for liquid water to exist on
the surface are needed for habitability,” said Gibson. “We only need to
look to Mars and Venus to see how differently terrestrial planets can
evolve. However, if the building blocks are there, then it’s more likely
that you will get Earth-like planets – and three times more likely than
we’d previously thought.”
Images
Rich spectrum of colours in the rocks around the Mutnovsky and Gorley
volcanoes on the Kamchatka Peninsula. The mineralogy of rocks on Earth
provide the chemical building blocks needed for life. Credit:
Europlanet/A. Samper.
https://www.ras.org.uk/images/stories/press/NAM_2015/Wednesday8July/Gibson.JPG
https://www.ras.org.uk/images/stories/press/NAM_2015/Wednesday8July/Gibson.JPG
In this artist's conception, gas and dust-the raw materials for
making planets-swirl around a young star. The planets in our solar
system formed from a similar disk of gas and dust captured by our sun.
Credit: NASA/JPL-Caltech. http://photojournal.jpl.nasa.gov/jpeg/PIA03243.jpg
Media contatcs
Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)794 124 8035
rm@ras.org.uk
Ms Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243
anitaheward@btinternet.com
Dr Sam Lindsay
Royal Astronomical Society
Mob: +44 (0)7957 566 861
sl@ras.org.uk
Science Contacts
Prof Brad Gibson
Director, E.A. Milne
Centre for Astrophysics University of Hull
Mob: +44 (0)7592 862768
brad.gibson@hull.ac.uk
Further information
The research on the Galactic Terrestrial Zone has been carried out by Brad Gibson, Chris Jordan, Kate Pilkingon, Marco Pignatari at the E.A. Milne Centre for Astrophysics at the University of Hull. http://www2.hull.ac.uk/science/physics/research/astrophysics-and-gravitation.aspx
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