Gliese 581c: our new home?
In the southern hemisphere, between the brilliant constellations of Virgo
and Scorpio, sits the Libra constellation.
His main stars, starting from the brightest one, are α Librae, also known as “southern
chela”, β Librae, also known as “chela of the north”, σ Librae and υ Librae.
Among the other stars, the following stand out:
γ Librae, that's an orange star, in the north-central part of the constellation;
HD 140283, which has an incredible age of about 14 billion years, so it's useful to
set limits on the age of the universe; Gliese 581, a red dwarf. Perhaps,
the most special one. Do you want to know why?
Follow me in this video to get to know more about Gliese 581 and exoplanets.
I promise you won't regret it!
On April 24 2007, it was discovered an exoplanet in the Libra constellation.
The discovery was announced by a team of astronomers from the
University of Geneva, Switzerland. At that time, the group was using the
HARPS instrument, installed in 2002 on the 3.6 m telescope of ESO La Silla observatory in Chile.
HARPS actually became operational in February 2003, and since then it was used to detect
exoplanets, based on measurements of the variations of the radial velocities of stars
subject to gravitational forces of bodies rotating around them.
Therefore, HARPS, which stands for High Accuracy Radial Velocity Planet,
was an amazing high precision spectrograph for radial velocities.
Astronomers that happened to use HARPS, were very lucky.
However, the planet was called Gliese 581c, because it is part of the Gliese 581 star system,
i.e. it orbits around Gliese 581. As we said in the intro,
Gliese 581 is a red dwarf star, that lies about 20 light-years distant from us.
Do you know what a red dwarf is? A red dwarf is a very small
and cool type of star. Red dwarfs are by far the
most common type of star in the Milky Way, at least in the neighbourhood of the Sun.
Red dwarfs are also ideal targets for the search for low-mass planets where water could be liquid.
Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the
Sun. Planets lying in this zone are then more easily detected with the radial-velocity method,
the most successful in detecting exoplanets. Unfortunately, because of their low luminosity
(since a cooler star is less bright than a hotter star), red dwarfs cannot be easily observed.
From Earth, not one star that fits the stricter definitions
of a red dwarf is visible to the naked eye. According to some estimates, red dwarfs make
up three-quarters of the stars in the Milky Way. They have a surface temperature of about 2000K.
If the Sun was a red dwarf, and we lied at the same distance from it, i.e. 1 Astronomical Unit,
we'd probably die of cold. This is an important point. Later we will talk about it in more detail.
Anyway, the discovery was that Gliese 581c was orbiting its host star. But of course,
there was more than that. In fact, astronomers think
Gliese 581c is one of the most Earth-like planets outside our Solar System to date.
Here are some of his characteristics.
1) Gliese 581c is an exoplanet with a radius only 50% larger than the Earth.
This means that his radius is about 9500 km.
2) It is capable of having liquid water on its surface.
And we know that because this exoplanet completes a full orbit in 13 days, and it is 14 times closer
to its star than the Earth is from the Sun. This, considering the fact that its host star
is a RED DWARF, brings us to the conclusion that Gliese 581c is actually in the so-called
habitable zone, the region around a star where water could be liquid.
Once Gliese 581c was discovered, astronomers continued studying its characteristics.
Among others, they estimated that the mean temperature of this super-Earth lies between
0 and 40 degrees Celsius, which means that if there is water, it should be in a liquid state.
But it's not over! In fact,
3) This exoplanet should be either rocky or fully covered by oceans.
This is a strong result. Actually, our planet models predict that a planet with a radius
of only 1.5 times the Earth's radius, would have this property.
At first glance, we can say out loud that Gliese 581c is a very important planet.
Since water is a key element to host life, it could be that Gliese 581c
is home to some form of life. “Liquid water is critical to life
as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France).
"Because of its temperature and relative proximity, this planet will most probably be a
very important target of the future space missions dedicated to the search for extra-terrestrial
life. On the treasure map of the Universe, one would be tempted to mark this planet with an X."
We want to spend some words talking about how this discovery was made possible.
We said astronomers detected Gliese 581c using the HARPS instrument,
which uses the radial velocity method for hunting exoplanets. How does this method work?
"Before finding out the answer to this question, be sure to like or dislike the video so that we
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Imagine having a big magnet. Imagine it has a great weight.
Now put a smaller magnet next to him. What would happen?
If the north pole of the first magnet is directed toward the south pole of the second one,
then they will attract and become closer to each other.
Now imagine to fix the position of the bigger one, and let the smaller one rotate in a circular orbit
around it, with a high rotation velocity. You will notice some variation in the
velocity and position of the big magnet! This is pretty much what instruments like HARPS
do. They study variations of radial velocities of a star, due to planets orbiting around it.
Located on the ESO 3.6-m telescope at La Silla, Chile, HARPS is able to measure velocities with
a precision better than one metre per second (or 3.6 km/h)! HARPS is one of the most
successful instruments for detecting exoplanets and holds already several recent records.
The detected velocity variations in the case of Gliese 581c are between 2 and 3 metres per second,
corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals
could not have been distinguished from 'simple noise' by most of today's available spectrographs.
We could say HARPS is a unique planet-hunting machine.
HARPS is also very efficient in finding planetary systems, where tiny signals have to be uncovered.
The two systems known to have three low mass
planets - HD 69830 and Gl 581 - were discovered by HARPS.
Nowadays, astronomers are striving to find planets with the same mass
(or less) than Earth. This is because, of course, since we know Earth could support life,
it is natural to suppose that there's a higher chance to find it on Earth-like planets.
This is why HARPS is so crucial for us. We are confident that, given the results
obtained so far, finding a planet with the mass of the Earth around a red dwarf is within reach,"
affirmed Michel Mayor, who discovered the first exoplanet
orbiting a star similar to the Sun, and was awarded the Nobel Prize in Physics in 2019.
So here comes the big answer: could Gliese 581c become our nem home?
Well, I mean, it's a hard question. We know that our modern technology can't
bring us to another star system distant 20.5 light-years away.
Maybe in the future, it could become a reality. For now, the only thing we know
is that some potentially habitable planets exist out there,
and the only thing we can do is hoping one day we will find evidence for life on them.
So far, astronomers have found the total number of potentially habitable exoplanets is 60.
1 of them is subterranean, i.e. it has Mars-size. 23 of them are Terran (which means Earth-size).
And 36 of them are super terrain, which is to say Super-Earths or Mini Neptunes.
Researchers have also identified 24 planets that are "super habitable", i.e. that could offer
conditions more suitable for life than Earth does. Isn't it amazing?
"This video ends here! Thanks for watching everyone! What are your thoughts about this
one? Do you think Gliese 581c could become our new home? Let us know in the comment below!
See you next time on the channel!