One of the most intriguing exoplanets that’s been discovered recently is Proxima b. It’s
in a planetary system that by cosmic standards, is our next door neighbor.
Since its discovery, many new and exciting things have been uncovered about the planet, including
the possibility that it's an ocean world. And where there’s water, there could be life.
Are new telescopes about to discover if Proxima b could harbor life?
[INTRO]
Alpha
Centauri is located 4.37 light-years away from us.
This may seem far but it’s three times closer than the next Sun-like star.
The third brightest star in our sky is actually from a triple star system consisting of the
binary star pair Alpha Centauri A and B, and Alpha Centauri C or Proxima Centauri.
The two stellar companions, Alpha Centauri A and B are only about 23 astronomical units apart,
which by cosmic standards is fairly close to each other. By comparison,
the distance between the Sun and Uranus is about 19.8 astronomical units.
Both stars have quite a bit in common with our Sun. Alpha Centauri A is slightly more
massive and shines with yellow light about 1.5 times brighter than the Sun. Alpha Centauri
B has an orange hue and is slightly less massive than our star, and half as bright.
The Alpha Centauri pair is also about 5 billion years old, which is slightly older than the Sun.
The third component of the system, the red dwarf Proxima Centauri, is a small star,
with just about 12% the solar mass, and a radius of about 15% that of our Sun.
Its surface temperature is also low, just over 2,725°C [4,940 °F].
It’s this little star that’s located closest to the Sun,
at about 4.25 light-years, and it’s getting even closer. In about
27,000 years, Proxima Centauri will be a little more than just three light-years away from us.
But although it’s the closest star to us, the luminosity of the dim red dwarf is just
0.17% that of the Sun. At the same time, Proxima Centauri often shows off its stellar character
by flashing brightly in the sky. Scientists attribute the sudden bursts of brightness to an
increase in the star's magnetic activity. This also happens on Alpha Centauri B, but rarely.
In general, Proxima Centauri stays apart from its companions. It’s currently about
13,000 astronomical units away from the binary pair. Due to its remarkable eccentric orbit,
every 550,000 years, Proxima Centauri approaches the Alpha Centauri pair at a distance of about
4,300 astronomical units [0.07 light years], but it's still quite far away.
Scientists suggest that millions of years ago, the two Alpha Centauri stars captured
Proxima Centauri by gravitational pull. The Proxima Centauri star
has a few planets in its orbit. And one of these planets has fascinated astronomers.
This is Proxima b. Astronomers discovered it in 2016 using the Radial Velocity method.
It relies on the fact that a star doesn’t remain completely stationary when a planet orbits it.
The star will actually move slightly in a small circle because of the gravitational tug of
the smaller planets. Researchers use extremely sensitive spectrographs to track a star's light
spectrum. If there is a planet around a star, the star's light will appear slightly blue-shifted,
and then slightly red-shifted. If those shifts are regular and repeat in fixed intervals of days,
months, or years, then this shifting of light is almost certainly caused by
a planetary body orbiting around the star, and tugging it back and forth.
After carefully studying the exoplanet,
our closest space neighbor seemed to be similar to Earth! According to astronomers,
Proxima b could have about 1.3 times our planet’s mass, a radius of 1.1 Earths,
and a similar density. Scientists also believe it could be a rocky world, just like ours.
But there are also differences between Proxima b and Earth,
one of them being the location of the two planets in their solar systems. Proxima b
is much closer to its parent star, located only 0.05 astronomical units away from it.
This is closer than the distance from Mercury to the Sun [0.4 AU]!
But if this planet is so close to its star,
doesn't that mean it would be a fiery hell like Mercury?
Because Proxima Centauri is a faint red dwarf, the exoplanet receives just 60%
of the energy of its star as the Earth gets from the Sun. Proxima b, like Earth,
is in the habitable zone of its star. And this means protein life could potentially exist there.
But the main criteria for life to exist on a planet in the Goldilocks zone is that
it’s not too hot and not too cold for liquid water to exist on the surface.
The Proxima Centauri star strongly attracts the planet by gravitational pull,
and one side of the planet is always facing the star.
A similar thing happened to our moon when it became tidally locked to Earth.
The side of Proxima b that "faces'' the red dwarf is, of course, much hotter than its opposite
side. The temperature on the hotter side exceeds zero and allows the possibility of liquid water.
This was confirmed by two climate models of
scientists at the University of Exeter and the British Meteorological Office.
The climate models exceeded the boldest expectations of researchers, showing a very stable
climate on Proxima b, with conditions suitable for the emergence and development of life.
So is it possible that Proxima b can have liquid water, and therefore life?
Despite all the obvious advantages, Proxima b may be far from the perfect world for us.
Intense solar flares that erupt from the star can strip the planet of its atmosphere.
But as we know life is so diverse and adaptable, it can still exist even if it's bombarded with
mega-fluxes of radiation particles. In its early stages of development, the Earth also received
huge doses of ultraviolet rays, and yet it has become home to a variety of living organisms.
The same scenario could be possible on Proxima b. Some astrobiologists say that even intelligent
life couldn’t be excluded as aliens might have built underground cities where the
deadly radiation couldn’t reach, or they could hide from radiation deep in bodies of water.
There are lots of examples of such life forms on Earth.
Coral polyps are extremely good at neutralizing the detrimental effects of ultraviolet light by
producing fluorescent proteins that block excessive sunlight. In shallow waters,
these organisms can glow a brilliant pink and purple at night. It’s possible that someday,
next-generation telescopes might be able to detect a similar glow in bodies of water on Proxima b.
If the planet lacks an atmosphere, the average temperature on Proxima b is
about -40°C [-40℉]. But if it has one, the temperatures there could reach 30°C [86℉],
which is warm enough to sustain liquid water on the surface.
The problem is, the nearby star still blows the planet's atmosphere into space.
However, scientists assume that Proxima b retained a part of its atmosphere. Especially if it managed
to form a thick gas cover around it when it was still young. Volcanic eruptions or comet impacts
can also partially compensate for the loss of the atmosphere by emitting gasses. Another suggestion
is that Proxima b is protected from radiation by a powerful magnetic field. Scientists hope
to test their theories with the 39-meter [128-ft] European Extremely Large Telescope.
It would be great to explore the system ourselves,
but even though the system is close to ours, it would take a very long time to get there. If we
tried to get to the Alpha Centauri star system by space shuttle, it would take 165,000 years.
But scientists have come up with an incredible plan that will allow them to get a good look at
the distant world without using telescopes. The Breakthrough Starshot program aims to send tens
of thousands of miniature space probes, weighing about 1 gram [0.002 lb] each, to Alpha Centauri.
In orbit, the probes will unfold huge solar sails made of thin foil
and measuring 4x4 meters [13x13 ft]. An Earth-based square-kilometer array of
lasers will aim streams of light at the sails, accelerating them to 20% of the speed of light.
Hopefully, the squadron can reach the Alpha Centauri system in just about 25 years. The
probes will collect valuable data and transmit it back to Earth. Once we receive it 5 years later,
we will be able to see what the legendary Proxima b is. Even though the date of launch
hasn’t been determined yet, several probes have already been successfully tested.
Meanwhile, in 2019, astronomers at the Astrophysical Observatory of Turin suggested
the existence of another planet there - Proxima c. Its mass is thought to be roughly 7 times that of
Earth’s, and depending on its size, it could be classified as a mini Neptune or a super-Earth.
According to astronomers' calculations, the planet is located at the outermost edge of
the planetary system and has an orbital period of more than five Earth years. Because of its
great distance to the star, the temperature on Proxima c is likely less than -234°C [-390℉].
According to some observations, the exoplanet has
an interesting feature. Proxima c is probably encircled with huge rings of
dust and asteroid debris which could be five times larger than Saturn's rings!
But this is not all the mysteries Proxima Centauri hides. Recently, scientists have discovered
another potential planet there. It was detected by the Very Large Telescope and named Proxima d.
The planet has a radius of 0.8 Earths and is considered one of the smallest exoplanets known to
mankind. But the mass of Proxima d, although four times smaller than Earth’s, is twice the mass of
Mars. For its tiny size, Proxima d is heavy, so scientists are almost certain that it is rocky.
The potential exoplanet is located at about 4.3 million kilometers [2.7 million miles] away from
the red dwarf. And that is more than ten times closer than Mercury is to the Sun!
Because of that, Proxima d makes a complete orbit around its star
in just five days. This is too close for life to exist on the
planet. Although it’s possible that some microorganisms could be hiding underground.
To figure this out, and learn about all the other secrets of our stellar neighbors,
scientists hope to use a new generation of telescopes. The famous James Webb telescope
already sends us its first images. And in 2023, the Telescope for Orbit Locus
Interferometric Monitoring of our Astronomical Neighborhood is scheduled to be launched.
It will specialize in observations of the Alpha Centauri system and its nearest stars.
What discoveries would you like these telescopes to make? Let us know with a comment and,
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