The most extreme exoplanets in the universe
To date, more than 4000 exoplanets are known: that is, we know over
4000 planets in orbit around stars other than our Sun! And in this video we will offer
you a review of the most extreme and curious exoplanets or the
first discovered exoplanets of their type known so far. Are you are ready? Let's go!
The first planets discovered around a pulsar Contrary to popular belief, 51 Pegasi b was not
the first exoplanet discovered: in 1992 Aleksander Wolszczan and Dale Frail announced the discovery
of two rocky planets around the pulsar PSR B1257 + 12, in the constellation of Virgo. A third planet
was later discovered. The importance of this discovery lies in the fact that at the time it
was not expected that planets could exist around pulsars, but only around main sequence stars.
Since they are constantly bombarded by radiation from the neutron star around which they orbit,
they are not suitable for hosting life forms. If they were in the Solar System,
the two outermost planets (PSR B1257 + 12 c and PSR B1257 + 12 d) would be more or less
at the same distance as Mercury from the Sun, i.e. about 0.3 astronomical units,
while the innermost planet (PSR B1257 + 12 b) would be just one third of this distance.
The first exoplanet discovered in a globular star cluster and the oldest planet
In 1993 the planet PSR B1620-26 b was discovered: it orbits a binary system
formed by a pulsar and a white dwarf, located in the direction of the constellation of Scorpio.
Its mass is 540 times that of the Earth and a size between 1.7 and 2.5 times that
of Jupiter. It takes about 68 Earth years to travel a single orbit around the star:
in other words, a 68-year-old person on Earth, on this planet would be only one year old! PSR
B1620-26 b is also known as Methuselah, because it holds another record: the oldest planet!
In fact, it is estimated that it has a venerable age of 12.7 billion years.
The first exoplanet discovered around a main sequence star
Didier Queloz and Michel Mayor in 1995 announced the discovery of the first planet orbiting a main
sequence star, 51 Pegasi: this star, also known as Helvetios, has nearly the same mass as our Sun,
although it is slightly larger than the our star. The planet, called 51 Pegasi b or Bellerophon,
has a mass half the mass of Jupiter and a radius 1.5 times that of the gas giant, and takes just
4.23 days to make one revolution around its star! It is located just 0.0520 astronomical units from
the star: if it were in the Solar System, it would be almost 6 times closer to the Sun than Mercury!
The first planet discovered through the transit method
In 1999 the research groups led by David Charbonneau and Greg Henry independently
discovered, through the transit method, a transiting planet in front of the star HD
209458 in the constellation of Pegasus, called HD 209458 b (remember that exoplanets are named
with the name of their star to which a letter of the alphabet is added starting from b).
The idea behind the transit method is to study the brightness trend of a star over time:
if you notice a periodic decrease in brightness by the star, it means that a planet is passing
in front of it, thus blocking a small part of the light coming from the star.
Its distance is 150 light years from Earth, and it orbits just under 8
million kilometers from its star; it is a "chthonic" planet, that is,
a gas giant that has practically lost all of its atmosphere based on hydrogen and helium,
due to the extreme proximity to the star, whose radiation has torn away the planet's atmosphere.
The first planet discovered within the habitable zone
In 2001 a group of astronomers from the University of Geneva discovered the first exoplanet,
HD 28185 b, in the habitability belt. The habitability belt is the area around the
star where a planet can keep liquid water on its surface and temperatures that are neither too high
nor too low. The planets in the habitability belt are very interesting because they are potentially
suitable for hosting life forms. What do you think the hypothetical inhabitants of
this planet might look like? Write it in the comments! However, consider that this planet
is most likely a gas giant slightly larger and 6 times more massive than Jupiter ...
The first Earth-sized exoplanet in a habitable zone
Discovered in 2014, Kepler-186f is 10% larger than Earth, and orbits a M1 spectral type
red dwarf star, half the size of the Sun, 492 light-years from Earth. Kepler-186 orbits just
0.052 astronomical units from its star: therefore very close to its star, much more than Mercury is
near to the Sun! Like HD 28185, Kepler-186 f may also have liquid water on the surface;
but since it orbits a much colder red dwarf star than the Sun, the circumstellar habitable zone
is much closer to the star. Among other things, if vegetation existed on this celestial body,
in all likelihood the leaves would be red, precisely because its Sun is colder than ours!
Can you imagine it? What would it be like to live there? Write it in the comments!
The closest exoplanet The existence of planets around Proxima Centauri,
the closest star to the Sun, already predicted in many science fiction movies and novels,
became reality in 2016 with the discovery of Proxima Centauri b:
only 4.3 light years away from us, of rocky type and slightly more massive than the Earth,
it travels its orbit in just 11 days, very close to its star.
Getting there, however, would not be trivial, because, even if it is only 4.3 light years away,
it would still take some time to get there: by plane it would take roughly 5 million years ...
First example of a circumbinary planet discovered with the transit method
Discovered in 2011, Kepler-16 (AB) b is a circumbinary planet, meaning it orbits two stars!
The orbits of the two stars of the binary system with respect to their common center
of mass are inclined with respect to the planet's orbit by just half a degree:
this indicates that the planet probably formed in a disk of circumbinary dust and gas.
The orbital period of Kepler-16 (AB) b is 229 days, very similar to the period of revolution of
Venus around the Sun, its mass is about one third of that of Jupiter and it is barely smaller than
Saturn. The two stars that make up the binary system are an orange star of spectral type K,
just over half the size of the Sun, and a red dwarf of spectral type M,
approximately one fifth of the size of the Sun. Would you like to live on this planet and
admire the sunset of its two suns, just like on Tatooine from Star Wars? Write it in the comments!
The most crowded exoplanetary system This record does not concern a single
exoplanet, but an entire planetary system, the one discovered around the star HD 10180,
128 light years from Earth in the direction of the southern constellation of Hydrus,
around which 9 planets would orbit, one plus than our Solar System! HD 10180 is a solar type star
but a little older than the Sun, because it is 7.3 billion years old while the Sun is almost 5
billion years old. HD 10180 b, the closest to its star, is 0.02 astronomical units from it,
while the farthest, HD 10180 h, is 3.4 astronomical units away from the central star:
if they were in the Solar System, HD 10180 b would be much closer to the Sun than Mercury,
while the other would be between the asteroid belt and Jupiter! So the HD 10180 system is
crowded both for the number of its planets and for the mutual proximity between them!
However, this record is controversial, because there are still doubts about the
actual existence of the planets HD 10180 b, HD 10180 i and HD 10180 j.
So really the current undisputed holder of the title of the most crowded exoplanetary system is
the system of the star Kepler-90, slightly larger than the Sun, at 2500 light years,
in the constellation of the Dragon: 8 planets, all discovered through the transit method and
confirmed. Only Kepler-90 h is in the habitability range. Again, if they were in the Solar System,
they would all be concentrated between an area between Mercury and the Sun and the Earth! It
is believed that Kepler-90 b, Kepler-90 c and Kepler-90 i are rocky planets or at the limit
super Earths, while Kepler-90 d, Kepler-90 e and Kepler-90 f could be mini Neptune and
finally Kepler-90 g and Kepler-90 h could be gas giants resembling Jupiter or Saturn.
The darkest exoplanet The holder of this curious record is the exoplanet
TrES-2 b, which orbits a star in the Dragon 750 light years from Earth. Discovered in 2006,
the acronym TrES-2 b indicates the Trans-Atlantic Exoplanet Survey, a survey aimed at searching for
exoplanets through the transit method carried out jointly by the Palomar Observatory in California,
the Lowell Observatory in Arizona and the Teide Observatory in the Canary Islands. TrES-2 b is
an alien world the size of Jupiter, and just 5 million kilometers away from its star. Unlike
Jupiter, however, it is at least as dark as coal, to the point that it has been nicknamed
"Coal Black": it reflects less than 1% of the light from its star! But why is it so dark? A
possible explanation is contained in the extremely close distance of the star around which it orbits,
a solar-type star: this causes the temperature of TrES-2 b to be very high, above 980 degrees.
Too hot to allow the formation of ammonia clouds, as is the case on Jupiter, instead, there are,
among the constituents of its exotic atmosphere, chemical compounds capable of absorbing light,
such as sodium and potassium vapors, or titanium oxide in a gaseous state.
TrES-2 b is probably in synchronous rotation with its star, that is,
it always shows the same face to it, a bit like the Moon does with the Earth.
55 Cancri e “Janssen”, the planet Mustafar from Star Wars
55 Cancri e, renamed Janssen following the NameExoWorlds competition launched
by the International Astronomical Union, is a super Earth with a mass equal to 8 times and
a radius equal to twice the similar quantities of our planet. It orbits the star 55 Cancri A,
a star just smaller than the Sun, in less than a day, about 2.3 million km from its star:
a distance only 6 times greater than the distance Earth - Moon! 55 Cancri e is known
for its extreme variations in brightness, the cause of which is not known exactly,
but could lie in large-scale volcanic activity on the planet: a landscape that will surely
remember the planet Mustafar to Star Wars fans, the planet in the Outer Rim of the Galaxy, home
to a long duel between Obi-Wan Kenobi and Anakin Skywalker, which ended with the latter's defeat!
Gliese 1214 b, Miller's planet of Interstellar Discovered in 2009 through the transit method,
Gliese 1214 b orbits a red dwarf star in the constellation of Ophiuchus only 40 light years
away from us and could be an "ocean planet" with oceans tens of km thick and an atmosphere of H and
He 200 km thick. It has a mass 6 times greater than that of the earth and a diameter almost 3
times greater than that of our planet, and orbits its star in a day and a half. For science fiction
fans this planet will surely remind Miller's planet that is explored by astronauts in the
movie Interstellar. For those of you who practice surfing: would you like to surf on the gigantic
waves of Gliese 1214 b? Write it in the comments! Kepler-37 b, the smallest
We conclude our review of exoplanets with Kepler-37 b, the smallest known exoplanet: it
is just as big as our Moon! It orbits a slightly smaller star than the Sun in 13 days, at an
average distance of 15 million km (about one third of the distance between Mercury and the Sun).
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