EXO-PLANETS
Are we Humans alone in the Universe?
We human beings have been wondering for centuries – Do we have more of them like us? The centuries-old quest for other worlds like our Earth has been rejuvenated by the intense excitement and widespread interest surrounding the discovery of hundreds of planets orbiting other stars by NASA's discovery program; the Kepler telescope launched on 7 March 2009, 3:49 am. The Kepler telescope's sole purpose, which contained the most extensive primary mirrors back then and a 96 Megapixel camera, was to detect the stars and exoplanets (extrasolar planets) outside our solar system. As per current data (28 January 2021), a total of 530,536 stars and 4,341 exoplanets have been discovered!
Question:- Why are there so
many stars than planets?
Well, I feel that
since stars on an average have luminosity billion times greater than planets,
gathering information about them from extremely far distances is much easier
and can be found by direct (coronagraph) method. However, planets being
extremely small in size and not having their own light could not be detected by
direct methods. Thus, millions of exoplanets are unknown to us…
Here is one of the most famous quotes that Sir Isaac Newton told that I agree wholeheartedly –
Before diving into the world full of amazing and
unimaginable exoplanets, lets understand how exactly did we find about them in
the first place. The Kepler telescope used the renowned Doppler's method (radial velocity method)
to determine the terrestrial body's speed. The Transit method was used to detect exoplanets'
presence, and we have also gathered information like their mass, radius, matter
they are made up of, and much more things. In simple words, the Transit method
makes use of the mini solar eclipse, i.e., when the exoplanets come right in
front of their host stars from our point of view. In such a case, the star's
luminosity reaching us dims for a certain amount of time. Wow! We found a planet!
But… what if it was a comet or an asteroid? For the same reason, we check for
the period after which we observe the same phenomena. Now one might think that
what if multiple planets are orbiting the same star? The amount of light
blocked by a certain planet is directly proportional to its size, so the
percentage of light blocked is traced. This not only tells us about the number
of planets but also the time period of each and measure of the semi major axis
of the elliptical orbits using Kepler's third law which states that the square
of time period is proportional to the cube of semi major axis of the orbit in
which that planet is moving in. Even if we encounter two planets of same size
in different orbits, as the distance from host star is different, the amount of
light blocked will still not be the same.
Question to think: What if there are
two planets of same size orbiting in the same radius and thereby having same
time period? This can highly be misunderstood by a planet with greater speed!
Fact: The intensity
with which light reduces during transit is extremely less. For Earth it is only
0.0084% of the total light of sun (You can get it by the ratio of planet area
to that of the host star, for Earth, diameter of sun is approximately 108 times
that of Earth).
So let us begin our
journey through some of the most interesting and weird behaving exoplanets,
that we might have just dreamt of :-
HD 189733 b –
This exoplanet has bluish colour similar to that of Earth. It
was the first-time scientists had measured colour of a planet back in 2005.
Whenever the planet went behind its host star, the blue spectrum radiation
became lesser, the other colours remaining approximate the same. Whereas when
it came back in our line of vision, again the blue spectrum of light increased.
Why though? Does this tell that there could be life on it as well? Well, here
comes the interesting part. The planet's blue colour doesn't come from water
rather it comes from the silicate
particles from the cloud condensed with the atmosphere's heat and
pressure, which forms glass shards giving the blue tint. Not only that, the wind speed here is around
2km/sec! Well, that is around 6 times the speed of sound! Being very
close to its host star HD 189733, its surface temperature is as high as 973 degree
Celsius!
This exoplanet always
has its one face facing towards its host star, and that's the reason, the
probable temperature on its "day-face" is above 2,000 degrees, but
minus 200 degrees on its night face! This is the reason why this planet rains rocks! Yeah,
the magma erupted on the hotter side vaporizes (Corot 7b revolves around its
host star only at a distance of 1.6 million miles, 22 times closer than Mercury
orbits the sun) which condenses on the colder side. Thereby raining rocks.
55 Cancri e –
55 Cancri e is a potentially carbon-rich planet, so high in temperature
and pressure that its interior could contain a large amount of diamond. Some interesting
facts about the planet are that the amount of diamond estimated is so high that
its total price would be in nonillions at the current diamond prices. There is
still debate about the atmosphere and rocky content on this planet as concrete
information is not available due to its thick layered atmosphere.
TreS-2b –
Cambridge, MA -
Astronomers have discovered the darkest known exoplanet - a distant, Jupiter-sized gas giant
known as TrES-2b. Their measurements show that TrES-2b reflects less than one
percent of the sunlight falling on it, making it blacker than coal! Initially,
scientists misunderstood it by a black hole, however, by further studying this
body, it was realized that maybe due to high concentration of Sodium and
Titanium oxides (eg. Ti3O5) which absorb most of the light, rarely the light
escaped this exoplanet. Another theory stating that the absence of ammonia
clouds needed for gas planets like TreS-2b to reflect light is the reason. Or…
could it be some advanced technology of Aliens on that planet…
WASP-17b –
It is the first planet discovered to
have a retrograde orbit,
meaning it orbits in a direction counter to its host star's rotation.
Question:- Upon searching
more on retrograde motion, I see that it is a mere effect of relative motion.
So is it the same here that we see WASP-17b in retrograde motion because of our
perspective? According to me, analogy doesn't fit here because almost all
exoplanets will undergo retrograde motion from our point of view. So how and
why does an exoplanet undergo retrograde motion?
It also has been
predicted that this exoplanet will change its direction of revolution n future.
Question:- How is it possible
for a planet to stop even for milli milli milli second. The centripetal force
will become zero and its host star will immediately attract the planet.
Apart from this it
has other characteristics like being 19 times in size of Jupiter but having
just half the Jupiter mass! So light in weight, that it is categorized as a
Pluffy planet.
KOI-5Ab –
Astronomers had
initially given up on the KOI-5A system of stars due to its complicated behaviour.
Thanks to NASA's second planet-hunting mission, the Transiting Exoplanet Survey
Satellite, or TESS, aided in untangling all evidence regarding KOI-5Ab. It was
realized that the KOI-5-star system consists of three stars, two of which are twin stars and orbit
each other every 30 years and the third one orbits these 2 with period of 400
years. The system hosts one known planet, called KOI-5Ab, a gas giant also
termed as hot Jupiter, comprises Hydrogen and Helium gases in excess. We can
see the reason why astronomers got confused. The transit method couldn't give
accurate result due to presence of 3 stars in the system.
Interesting fact:- There can be ice
even when the exoplanet is between the star and goldilocks zone. This is
possible only if the gravitational pull of the planet is very large, which doesn’t
let water evaporate and thus leads to ice formation. Yes, ice. But if you even
try to touch this ice, you might burn severely! Such form of ice has been found
in Gliese 436 b and is called ice-10.
However that is not
the only condition. Another fact is that out of the 4,341 exoplanets
discovered, very few have been identified as exoplanets in the goldilocks zone.
Well, that doesn't end up here. Out of these a few have one face always towards
its host star and a few others are smaller version of Neptune rather than a
larger version of Earth and thus contain excess amount of hydrogen in their
atmosphere (for eg. K2-18b, which was initially widely declared to be as
habitable zone due to presence of water, which later was proved wrong). Also,
since most of these exoplanets have Red dwarf stars as their host stars, they
being highly active radiate large amount of UV rays, which again is unfavourable
for humans to live. So, let's have a look at those very few in which possibly
humans can live… or in other words, Aliens could be living or maybe our
ancestors could go (that's only possible if Einstein is proven wrong about
nothing moving faster than light and thus, we find a space machine)!
7. Kepler 186-f -
Nicknamed "Earth's cousin",
Kepler 186-f was declared as a potentially habitable zone in 2014, after
findings of the same by Kepler telescope. It also has a tilt from vertical
similar to that of Earth. Also, presence of rocky structure has been detected.
Thus, we have declared that life is highly possible there. However, since we
don't have technologies to dive deep into details of such planets located so
far, we can't say anything about presence of life there.
Kepler- 1649c –
The funniest fact
about this planet is that it was found coincidently! Yes. When looking through old observations
from Kepler, scientists discovered this planet, which the agency retired in
2018. While previous searches with a computer algorithm misidentified it,
researchers reviewing Kepler data took a second look at the signature and
recognized it as a planet. Out of all the exoplanets found by Kepler, this
distant world – located 300 light-years from Earth – is similar to Earth in
size and estimated temperature. It is 300 light years away from Earth, is about
1.06 times larger than Earth and receives 75% of light compared to what Earth
receives from sun. This makes favourable environment for existence of life.
Similarly, there are a more exoplanets, habitable for human beings known to us till date. However just like stars, the entire universe is filled with planets as well. Along with the Kepler telescope, Hubble Space telescope, Transiting Exoplanet Survey Satellite (TESS), Convection, Rotation and planetary Transits telescope and many more aided towards discovering exoplanets. Well, names of most of the stars are kept on the basis of the telescope that found them! Let me tell you another fun fact,
Fun fact:- The entire
universe is believed to be formed from matter and antimatter. All the planets
and stars and their compositions that we see are made up of matter. So where is
all the antimatter gone? Well, that remains a question till date though
scientists have created antimatter but in very very meagre quantities. So there
is a hypothesis that there could be an anti-world just like ours which we can’t
see. But yes, remember one thing, if you ever meet your anti-you, or two
planets and anti-planet meet, in one tiny glimpse both would vanish!
Gradually our quest is being satisfied
and we are getting more and more information about such planets. It is a huge
achievement of all the scientists to reach such a stage. I remind you, that the
habitable zones that we are in search of are for us human beings. However, we never
know about an altogether different race which requires different conditions to
survive! Yes, there
could be aliens in one of the exoplanets we declared to be inhabitable for us humans!
Maybe they breathe hydrogen (or maybe breathing is simply not a basic necessity
there), or silicon could serve as the fundamental element instead of carbon…
Really, anything can happen. Our main focus yet remains to get deep into the
planets we have characterized as habitable, and know if – “Are we humans alone
in this Universe?”
