20 years ago we only knew about ONE
habitable planet, today we know there
CAN WE FIND ANOTHER
EARth. THE ONLY
When you think about the Universe and its enormity do you ever come to think about the existence of
other life forms? Considering how many solar systems and planets there are, is it so unbelievable that
we might not be alone? Have you ever thought about the possibility of other human colonies? Well, in
the last couple of years cosmologists have found many Earth-like planets, which might be able to sup-
port life, or planets that we could travel to and establish new colonies on. If you are looking for answers
to these questions, this is the place, but before we dive into the depths of the Universe, let’s take a look
at some of the basics.
Exoplanets are celestial bodies which orbit around stars other than our Sun. These so called exoplan-
ets, especially habitable ones, are of extreme interest to scientists - ﬁnding out if there is life on them,
or if they have the right conditions to support life. According to the latest information our best guess
is that most of the stars in the Milky Way have planets, and roughly 20% of those planets are habit-
able. Astronomers take a closer look at these exoplanets and look for particular ones that fall into the
Goldilocks zone. The Goldilocks zone is region of space in which a planet is just the right distance from
its home star so that its surface is neither too hot nor too cold. If these planets have high enough tem-
perature and atmospheric pressure to allow liquid water on their surfaces, a new habitable exoplanet is
found. Just qualifying a planet as habitable isn’t enough. It doesn’t mean that it offers the right condi-
tions to sustain intelligent life forms. Additionally the planet must be far enough away from the galactic
center to avoid destructive radiation.
AND WHY ARE WE INTERESTED IN THEM?
Since most of our galaxy’s stars
are red dwarfs, scientists are
looking for exoplanets around
them too. Red dwarfs are smaller
compared to other stars, emit
less light and are not really vis-
ible in the night sky.
There are three times more of
them than any other type in our
galaxy. The reason for being
so fascinating is that each red
dwarf has at least one planet
on average, many of which are
Earth-sized. Another factor that
makes these celestial bodies
exceptional is that it’s easier to
track planets around them, caus-
ing a larger drop in the relative
brightness of their star making
them easier to detect.
Are any different than
our solar system?
How many habitable
planets are there?
Well, it all started about 20 years
ago when astronomers only
knew about one star that had
planets orbiting around it - that
star was our Sun. In 1995 every-
thing changed when cosmolo-
gists discovered a Jupiter-like
gas giant “51 Pegasi B”, which is
about ﬁfty light years away from
the Earth. Ever since then sci-
entists have been discovering
hundreds of exoplanets around
stars throughout our galaxy.
After some serious number
crunching, astronomers found
out that about 22% of stars,
which are similar to our Sun,
have at least one planet in the
Goldilocks zone. These planets
are usually about the size of the
How did exoplanet
DO SCIENTISTS USE?
Easy, they use telescopes. The most famous one being the
Kepler space telescope named after the famous German as-
tronomer Johannes Kepler. This $600 million telescope was
launched into space in March 2009 and its mission has been
incredibly successful, detecting more than 3,800 potential
exoplanets to date. After further analysis approximately 25%
of these were conﬁrmed as real.
CAN LIFE EXIST ON MOONS?
Who says that only planets are capable of supporting life? Some
moons may also offer a habitable environment and this is where it
gets even more interesting. Cosmologists found many gas giant
exoplanets that might have moons inside the Goldilocks zone.
So, what do cosmologists do?
Well, the telescopes monitor the
drop in a star’s brightness when
a planet crosses in front of it. This
phenomenon is called the “Tran-
sit”. If a drop in the brightness is
detected that means an exoplan-
et has been found in that solar
system, which makes it a region
of interest. This indirect method
of observation allows scientists
to calculate how big and how
dense the planet is with respect
to the size of its star. This method
presents us with an idea of dis-
tance, size and orbital period of
the planet, but cannot provide us
any detailed information about
the planet itself. However these
planets are so distant and hidden
from view, due to how small and
dim they are compared to their
parent stars, direct observation is
currently impossible. One of the
most popular exosystems that
scientists know of is the Kepler 62.
The Kepler 62 has two Earth-like
planets and is very similar to our
own Solar system, despite being
1200 light years away.
SO CLOSE ... YET
SO FAR AWAY
WHAT IS THE
TOO FAR AWAY...
NO PROBLEM, LIGHT TO
The direct exploration of exoplan-
ets is not an easy task as they are
just too far away to reach by any
existing spacecraft. Even for our
fastest probe, the Voyager, the trip
to our closest exoplanet would
take 200,000 years. We don’t
have any other options at the mo-
ment, except studying the light
that reaches us from the stars. So
how do we analyze it?
Join What is Universe in the adventure of discovering the future of exoplanet research.
Each planet’s atmosphere has its own ﬁngerprints
and that information can get to us as the star’s light
passes through the atmosphere during a planets
The most important element that scientists look for
is oxygen, one of the building blocks of life. Even
though that is deﬁnitely a good indication, scientists
have to remain cautious as some other factors may
also produce Oxygen, for example water vapor in the
upper atmosphere of a young planet could break
into hydrogen and oxygen by incoming strong ultra-
violet rays from the parent star.
Scientists are already building the next generation of
telescopes that may one day discover the ﬁrst habit-
able exoplanet. Such a discovery will ﬁnally provide
an answer to the fundamental question of whether
life exists beyond Earth.
How to study exoplanetary
atmospheres from earth?
More breakthroughs in
the near future