Not too cold, not too hot—the conditions for life are found
not just on Earth, but on a handful of other places out in
We Earthlings are a really lucky bunch. Our planet is located
in just the right spot in our Solar System. We’re not too close
to the Sun, like Mercury or Venus, where the average
temperature can reach more than 400°C. It’s not too far away,
either, like Jupiter or Saturn, where it can get really
cold—way under 140°C.
But our planet is not the only one with such ideal conditions.
A bunch of other planets and moons are also found in
the so-called habitable zone or Goldilocks zone. Planets or
moons located in the Goldilocks zone are at the right distance
from their star so that they’re not too hot and not too
cold—just like Baby Bear’s porridge in the fairy tale. Their
overall temperature is just right for the formation of liquid water, a landmark of life.
it is not just about being “in the zone”. Mars, for
example, is found within the habitable zone of our system, and
we have yet to find the first Martians.
Also, being in the habitable zone doesn’t mean they actually
have water, but they could. These potentially habitable planets
need to meet
other requirements to be able to host some sort of life,
like having an atmosphere, being a rocky planet (and not one
made up of gas) and having the right mix of chemical compounds
needed by living organisms.
Is there life out there?
This question has been in the mind of people for aeons, and
maybe now we are finally close to getting an answer. Several
celestial bodies, either planets or their moons, have been
identified as potential candidates to host life.
Some are planets around the same size of Earth, orbiting a star
much like our own Sun. Others are called super-Earth
planets and are as large as 45 times the size of Earth.
The most famous of these planets, arguably, is Mars, which made
some big news recently when it was confirmed it hosts a vast
amount of water just beneath its surface. The finding,
according to experts, means that Mars could one day allow for
the establishment of a human colony and perhaps even allow some
other lifeforms to exist.
“Certainly on Earth, we find life associated with big ice
sheets. So it doesn’t actually have to be liquid water in which
life can exist, and it would be very interesting to look at
where these ice scarps are melting,” Simon George, at Macquarie
“[The melting ice could] potentially expose new bits of ice and
possibly be a very interesting place to look for new evidence
of life, either in the recent geological past or even living
today on Mars,” George added in a recent
Beyond Mars, another place where scientists are pouring their
hopes are the moons from a big planet.
Life on a moon
Saturn, one of the largest planets of our solar system, has 62
moons, some of which are tiny moonlets just 1km
in diameter. Others are larger than some planets, like the
moon Titan, nearly half the size of Earth.
One of Saturn’s moons has been the focus of attention among
extraterrestrial life hunters: Enceladus. Here, scientists have
vast oceans of water, buried 30 to 40 kilometres beneath
the planet’s surface, which is covered in ice and snow and
where temperatures reach -198°C, at noon! The Cassini space probe
revealed the existence of all the vital ingredients for life in
these oceans: carbon, nitrogen and hydrogen.
“I think this is it. From an astrobiology point of view, this
is the most interesting story,” said Chris McKay, a planetary
scientist at NASA
in a recent news report.
Saturn is not the only planet with a moon that potentially
hosts life. Jupiter’s moon Europa has been a target for
exploration since the 1960s.
Made famous by the book (and movie) 2001: A Space
Odyssey, Europa has an ocean of liquid water lurking
beneath a layer of ice 15 to 20 kilometres deep. At least two
future NASA projects plan to explore this moon in more detail.
Life beyond our Solar System
Other stellar systems that host potentially habitable planets
have been identified in the past years.
Just last year, a study
reported the existence of a possible super-Earth planet, about
41 light years away from Earth. The planet, named LHS
1140b, is 1.4 times the size of Earth and twice as dense
and is found within the habitable zone of its star system.
“This is the most exciting exoplanet I’ve seen in the past
decade,” said lead author Jason Dittmann of the
Harvard-Smithsonian Center for Astrophysics in a press release.
“We could hardly hope for a better target to perform one of the
biggest quests in science—searching for evidence of life beyond
However, nothing yet is known about the inner components of
“Right now, we’re just making educated guesses about the
content of this planet’s atmosphere,” said Jason.
“Future observations might enable us to detect the atmosphere
of a potentially habitable planet for the first time. We plan
to search for water, and, ultimately, molecular oxygen.”
The planet 1140b was discovered through the MEarth
project, which seeks to identify Earth-like planets.
Besides 1140b, the MEarth project has so far discovered two
other Earth-like planets, GJ1132b,
Another stellar system that has revealed the existence of
potentially habitable planets is called TRAPPIST-1. The system,
39 light years from our planet, is located in the constellation
Aquarius, and recent observations have revealed the existence
of at least seven small planets orbiting the central star of
this system. Out of these seven, three planets
are found in the habitable zone.
“This is an amazing planetary system, not only because we have
found so many planets, but because they are all surprisingly
similar in size to the Earth!” said Michaël Gillon, at the
University of Liège in Belgium, who led
the 2016 study, in a press release.
Two of these planets, TRAPPIST-1b and TRAPPIST-1c,
were further studied and are likely to be rocky planets,
like Earth, which makes them even better candidates for hosting
Other potentially habitable planets have been identified by
space telescope. One of these planets, Kepler-452b, is
located in the constellation Cygnus, with a star very similar
to our own sun. The planet is about 60% larger than Earth, but
whether it is a rocky planet or if it contains liquid water is
still a mystery.
“We can think of Kepler-452b as an older, bigger cousin to
Earth, providing an opportunity to understand and reflect upon
Earth’s evolving environment,” said Jon Jenkins, from NASA’s
Ames Research Center,
in an official press release.
“It’s awe-inspiring to consider that this planet has spent 6
billion years in the habitable zone of its star; longer than Earth.
That’s substantial opportunity for life to arise, should all
the necessary ingredients and conditions for life exist on this
planet,” he added.
Life as we know it
But how do you really know if a planet can host some
sort of life? Until you actually find some alien life form, it
is all really theoretical. But now, a new study just published
found solid evidence that one species of microorganism could
survive in Saturn’s moon Enceladus.
The compounds found in Enceladus, such as methane, carbon
dioxide, ammonia and hydrogen, can be either produced or used
for growth by microorganisms.
this new study,
researchers managed to grow microorganisms under the gas and
pressure conditions thought to be present in Enceladus.
Researchers found one survivor: a microorganism capable, in
theory, of surviving in Enceladus, even under the presence of
nasty compounds that would inhibit the growth of other life.
“The microorganism Methanothermococcus okinawensis
thrives and produces methane under conditions similar to those
found in Saturn’s icy moon Enceladus,” says Simon Rittmann, at
the University of Vienna, who led the new study.
Furthermore, researchers identified a geological process known
serpentinisation, which might produce enough hydrogen for
the survival of some kind of lifeform on Enceladus.
The findings support the idea that certain microorganisms can
thrive in Enceladus and be responsible for some of the methane
detected in this moon.
But will we ever find some sort of intelligent life? Some
scientists think so, and the reason is simple: odds are on our
side, sort of.
It is a big, big universe with trillions of planets and stars,
and we already know many moons and planets very like Earth have
the right conditions for life as we know it. So why not?
“In the search for life in the Solar System and beyond, the
physiological capabilities of several organisms found on Earth
that live or survive under extreme environmental conditions
make it likely that, somewhere in the universe, alien life
could exist . It could be possible that we might find life just a doorstep away,” says Simon.
on other planets could be far more widespread, study finds