Water Worlds!

Post Reply
User avatar
Wade Hampton III
Posts: 2339
Joined: Fri Oct 18, 2013 10:40 pm
Location: Pontiac, SC

Water Worlds!

Post by Wade Hampton III » Sun Sep 02, 2018 6:35 pm

by Matt Williams

Ever since the first exoplanet was confirmed in 1992, astronomers have found
thousands of worlds beyond our Solar System. With more and more discoveries
happening all the time, the focus of exoplanet research has begun to slowly
shift from exoplanet discovery to exoplanet characterization. Essentially,
scientists are now looking to determine the composition of exoplanets to
determine whether or not they could support life. A key part of this process
is figuring out how much water exists on exoplanets, which is essential to
life as we know it. During a recent scientific conference, a team of scientists
presented new research that indicates that water is likely to be a major
component of those exoplanets which are between two to four times the size
of Earth. These findings will have serious implications when it comes to the
search for life beyond our Solar System. The research was the subject of a
presentation titled “Growth Model Interpretation of Planet Size Distribution“,
which took place at the 2018 Goldschmidt Conference in Boston. During a session
titled “The Role of Extreme Atmospheric Escape from Hot Exoplanets“, the team
presented findings that indicated that water worlds may be more common than
previously thought.
57035
Sunset
Sunset
57035.JPG (39.58 KiB) Viewed 1254 times
These findings were based on data from the Kepler Space Telescope and Gaia
mission, which were analyzed by an international team of scientists led by
Dr Li Zeng – a researcher from Harvard University’s Department of Earth and
Planetary Sciences. As they indicated, the Kepler mission has precisely
measured the radii of over 4000 exoplanet candidates, along with their
orbital periods and other parameters. These exoplanet candidates can be
divided into two size categories: those that have 1.5 times the radius of
Earth, and those that average around 2.5 Earth radii. Combined with mass
and recent radius measurements from the Gaia mission, the team was able to
develop a model of these planets’ internal structure. Whereas planets that
fall into the former category are believed to be rocky, the latter ones are
generally thought to range from super-Earths to Neptune-sized gas giants.

However, according to the model developed by Li and his colleagues, many of
the confirmed exoplanets that are between two to four times the size of Earth
may in fact be water worlds. On these planets, roughly 50% of the mass consists
of water, whereas water makes up just 0.2% of the Earth’s mass. As Dr. Zeng
explained during the course of the presentation:

“It was a huge surprise to realize that there must be so many water-worlds…
We have looked at how mass relates to radius, and developed a model which
might explain the relationship. The model indicates that those exoplanets
which have a radius of around x1.5 Earth radius tend to be rocky planets
(of typically x5 the mass of the Earth), while those with a radius of x2.5
Earth radius (with a mass around x10 that of the Earth) are probably water
worlds”. However, when one considers the orbital characteristics of these
planets (i.e. how closely they orbit to their respective stars), a very
interesting picture begins to emerge. As Li explained, these “water worlds”
are not so much rocky planets that are covered in deep oceans, but an
entirely new type of planet for which there is no equivalent in the Solar
System.
57036
Twin Moons
Twin Moons
57036.JPG (34.76 KiB) Viewed 1254 times
“This is water, but not as commonly found here on Earth. Their surface
temperature is expected to be in the 200 to 500 degree Celsius range,” he
said. “Their surface may be shrouded in a water- vapor-dominated atmosphere,
with a liquid water layer underneath. Moving deeper, one would expect to
find this water transforms into high-pressure ices before we reaching the
solid rocky core. The beauty of the model is that it explains just how
composition relates to the known facts about these planets.” Perhaps even
more surprising was just how common these planets appear to be. According
to their study, Li and his colleagues indicated that about 35% of all known
exoplanets that are larger than Earth should be be water-rich. What’s more,
they hypothesize that they likely formed in a way that is similar to how
the cores of gas giants are believed to have formed – a rocky core surrounded
by layers of volatile material made solid by pressure.

Naturally, this discovery has significant implicatios for when it comes to
the search for life beyond our Solar System. Until now, the idea that water
is essential to life as we know it has been a foregone conclusion to scientists.
But if this study is correct, then it appears that water is far more plentiful
on exoplanets than previously though, and could be an impediment to life as
we know it. If indeed water worlds consist of hot, steamy atmospheres, and
dense ice layers closer to their cores, then it would be difficult for life
to emerge on these worlds. Basically, the extreme heat and the a lack of access
to sufficient sunlight, hydrothermal activity and land masses would make for
a pretty hostile environment. Nevertheless, the study does offer some intriguing
possibilities when it comes to characterizing exoplanets and seeing what’s
out there.
57037
Facing Starward
Facing Starward
57037.JPG (42.24 KiB) Viewed 1254 times
Looking to the future, Li and his colleagues are hopeful that the newly-launched
Transiting Exoplanet Survey Satellite (TESS) will find many more of these water
worlds. This will then be followed up on by ground-based telescopes – and the
soon-to-be-launched James Webb Space Telescope (JWST) – which will provide
spectroscopic measurements that will help scientists characterize these planets’
compositions and atmospheres. As Professor Sara Seager (Jewess?),
a professor of Planetary Science at Massachusetts Institute of Technology
(MIT), and the deputy science director of the TESS mission, said:

“It’s amazing to think that the enigmatic intermediate-size exoplanets could
be water worlds with vast amounts of water. Hopefully atmosphere observations
in the future–of thick steam atmospheres—can support or refute the new findings.”

In the meantime, there are still plenty of rocky worlds out there to be
explored for signs of life!

Post Reply