[ Music ]
So when we think about ocean worlds, it's good to compare them to what
we know about Earth. In total proportion, Earth is about point-one-percent water.
An ocean world is a body that has, in proportion, about ten times more water
than Earth does.
And when we think of the TRAPPIST planets, those planets have about fifty times
more water in proportion to what Earth does.
Ocean worlds do appear to be common in our galaxy. As far back as the early 2000's,
We had astronomers, some of them still here at NASA Goddard that suggested that we would
have ocean worlds orbiting low-mass stars.
Recently we've looked at about fifty-two exoplanets, and these are low-mass exoplanets
and what we've found is, of these fifty-two planets one out of every four
may be an ocean planet.
And when it comes to these ocean planets, over half of them may be ice-covered
ocean worlds, and so Enceladus and Europa may serve as small-scale analogues
of these planets.
So there are a number of different ways to search for life on planets around other stars,
but the key method is the study of the atmospheres.
We can search for signs of life - biosignatures, we call them, things like oxygen,
water vapor, carbon dioxide, even more unusual biosignatures -
things like chlorofluorocarbons, or other things that are only produced by intelligent life.
By looking for these key constituents of planetary atmospheres that signal life,
We can discover lifeforms on other planets that we could never actually visit in our lifetime.
So this is very analogous to how we study the atmospheres of moons and planets
in our own solar system, and really makes the connection between studying the plumes
of Europa, and the atmospheres of planets around other stars.
What I would like to see is the definition of a habitable zone expanded
We don't want to keep thinking too narrow about liquid on the surface, broaden the scope
and really try to embrace other worlds that might seem too far from their host star,
and frozen out, when they really aren't frozen at all. At great depths, they harbor
a warm, hydrothermal-driven, liquid water environment.
[ Music ]