- 3899 - EXOPLANETS - What are some of them like? Although astronomers have discovered more than 5,200 exoplanets, less than 200 are rocky, the rest are gaseous.
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3899 - EXOPLANETS - What
are some of them like?
-
- An exoplanet
“Wolf 1069 b”, orbits a red dwarf star, Wolf 1069 is only 31 light-years from
Earth. What makes this discovery particularly intriguing is that Wolf 1069 b is
potentially a rocky world, at about 1.26 the mass of Earth and 1.08 the size.
-
- Wolf 1069 b
also orbits in its star's habitable zone, making it a prime candidate for
liquid water to potentially exist on its surface. A planet of roughly Earth
mass orbits the star within 15.6 days at a distance equivalent to one-15th of
the separation between the Earth and the sun.
-
- The planet
Mercury, which is the closest planet to our sun, has an orbital period of 88
days. As a result, its surface temperatures reach as high as 800 degrees
Fahrenheit.
-
- Unlike
Mercury, Wolf 1069 b lies within its star habitable zone despite its much
shorter orbital period of 15.6 days. This is because its star is a red dwarf
star, meaning it's much smaller than our sun and Wolf 1069 b receives
approximately 65% of the solar radiance that Earth receives.
-
- This
improves its prospects for habitability, with relatively desirable surface
temperatures that range between minus 139.27 degrees Fahrenheit and 55.13 F , with an average of minus 40.25
F.
-
- One unique
feature of Wolf 1069 b is that it is tidally locked to its parent star, meaning
one side is always in daylight and the opposite side is always in
darkness. This attribute is shared by
the moon in its orbit around Earth, as well as with most habitable exoplanets
orbiting red dwarf stars.
-
- While tidal
locking means the planet doesn't have a day/night cycle like Earth, the
researchers hope that its dayside could still boast habitable conditions.
-
- The
remarkable discovery was made possible with the CARMENES (Calar Alto
High-Resolution Search for M Dwarfs with Exoearths with Near-infrared and
Optical Échelle Spectographs) instrument on the 11.5-foot (3.5-meter) telescope
at the Calar Alto Observatory in Spain.
-
- CARMENES
can observe astronomical objects using two separate spectrographs in both the
visual and near-infrared channels. The instrument discovered Wolf 1069 b using
the exoplanet detection method known as “radial velocity”, which detects small
wiggles in a star's location caused by a planet's gravity.
-
- Given its
relatively short distance from Earth of 31 light-years, Wolf 1069 b is now the
sixth closest Earth-mass habitable zone exoplanet; the others are, in order of
increasing distance,
-
-------------------
Proxima Centauri b,
-------------------
GJ 1061 d,
-------------------
Teegarden's Star c,
-------------------
GJ 1002 b and c.
-
- We found
that Wolf 1069 b is not a transiting planet, and for this reason, we won't be
able to further characterize its atmosphere using the 'transmission
spectroscopy method'.
-
- To
characterize the atmospheres of RV-only detected planets is absolutely crucial,
as many of these intriguing worlds that are closer to us are also RV-only
detections.
-
- There are
several ways that exoplanet discoveries are made. The most obvious way to find
an exoplanet is to see it directly using a telescope. Distant planets are so
faint they are usually lost in the bright glare of their host stars. This
approach has been successful in some cases.
-
- The
majority of exoplanets have been found by “transit”, which involves looking for
a slight dimming of the host star as the planet passes in front of it. This can only be used if the geometry of the
planet's orbit allows us to see the transit from Earth.
-
- As a planet
orbits around a star it causes the star to wobble slightly. In principle, using
a precision measuring technique called “astrometry”, this wobble can be
observed directly. It was the first exoplanet detection method to be tried, but
has only been successful in a handful of cases.
-
- It is much
easier to detect the tiny wobble caused by an orbiting planet by looking at a
star’s velocity rather than its position in the sky. This can be done using
spectroscopic techniques, and the resulting "radial velocity" method
has been very successful at detecting exoplanets.
-
- The final
method of discovery is called gravitational microlensing and requires
Einstein’s theory of relativity. This shows how light from a distant object is
bent as a star passes between it and the observer. The pattern of bending is
slightly different if there is a planet orbiting the star.
-
- A PLANET
WITH TWO SUNS: TIC 172900988. NASA’s top
planet hunter at the moment is TESS, the “Transiting Exoplanet Survey
Satellite”. This detects exoplanets by measuring the slight dimming of their
host stars when a planet crosses the telescope’s line of sight to them.
-
- This can be
a slow process, because astronomers may need to observe several transits to get
a full picture of the planet's orbit,
and there may be months or years between transits, depending on how
rapidly the planet orbits.
-
- But in the
case of TIC 172900988 b, the whole process was super-quick. That's because it
orbits two stars and TESS saw it transit across both of them. It also observed
no fewer than three mutual eclipses between the stars themselves. Putting all
this information together gave researchers everything they needed to calculate
the orbit in detail.
-
- BROWN DWARF
PLANET: Brown dwarfs are enigmatic
objects that are neither stars nor planets. With just 15 to 75 times the mass
of Jupiter they’re unable to sustain the fusion reactions that make stars
shine, yet they’re found in the depths of space, rather than orbiting around a
star like planets do.
-
- Brown
dwarfs are sometimes found in pairs, but it's only recently that one was
discovered with what appears to be an honest-to-goodness planet orbiting around
it. The brown dwarf in question and its planetary companion , possibly as small as 4.1 Jupiter masses, was
spotted in images taken by the Hubble Space Telescope.
-
- PROXIMA
CENTAURI C. The sun's nearest cosmic
neighbor is the red dwarf Proxima Centauri, 4.25-light-years away. There was a
flurry of excitement in 2016 when a planet was found orbiting this star. It was
a particularly significant discovery, because the planet appears to be similar
in size to Earth and is located in the star’s habitable zone, meaning that it
might potentially harbour life.
-
- Then in
2020, astronomers announced the likely discovery of a second planet in the same
system. Proxima Centauri c, is less
likely to be habitable, orbiting so far out that it receives very little of the
star’s warmth.
-
- HD 108236
B. This is one of the most interesting
discoveries made by TESS in 2020 was a family of four planets orbiting a
sun-like star. Described as "a super-Earth and three sub-Neptunes",
these cover a range of planetary sizes not found here in the solar system,larger
than Earth but smaller than Neptune.
-
- The
innermost of the four planets is over three times the mass of our own planet ,
this orbits 22 times closer to its star than Earth is to the sun. This gives it
an amazingly short year of just 3.8 days, and makes it too hot to inhabit. NASA
estimates its surface temperature at a scorching 1,500 degrees Fahrenheit.
-
- HD 106906 B
is a huge planet, around 11 times the mass of Jupiter, is one of the few
exoplanets to be discovered by direct imaging.
It was originally found in 2013 by the Las Campanas Observatory in
Chile, but it wasn’t until 2020 that details of its orbit were worked out using
data collected by NASA’s Hubble telescope.
-
- It turned
out to be a truly extraordinary orbit, almost 68 billion miles out from its
host binary star, which is 730 times further than the distance between Earth
and the sun. This huge orbit gives the planet an incredibly long year of the
order of 15,000 Earth years.
-
- AN
EARTH-LIKE MICROLENSED PLANET. To date,
around 120 exoplanets have been found by the gravitational microlensing
technique. Many of these bear the quirky-looking prefix OGLE, because they were
detected by the Optical Gravitational Lensing Experiment. One of the most
recent discoveries is particularly significant because it is the smallest
planet yet found by this method.
-
- Its
discoverers estimate it to be between 1.4 and 3.1 times the mass of the Earth,
and to orbit a star smaller than our own at a distance 1.2 to 2.3 times the
Earth’s distance from the sun.
-
- SPOTTED BY
A RADIO TELESCOPE, astrometry is one of the trickiest methods used to find
exoplanets, involving very precise measurements of the position of a star to
detect the tiny wobble caused by an orbiting planet. It's normally done using
optical telescopes, but in 2020 the first astrometric detection was made via
radio astronomy.
-
- This used a
continent-wide network of radio telescopes stretching between Hawaii and Puerto
Rico to detect a Saturn-sized planet orbiting around an ultra-cool dwarf star.
Researchers used the measured wobble to establish that the planet has an
orbital period of approximately 221 days.
-
- Most of the
exoplanets found so far are relatively nearby in cosmic terms, generally within
about 3,000 light years. That's still
well within our own Milky Way galaxy, but there must be countless exoplanets in
other galaxies too. The first of these was discovered in 2020, in the Whirlpool Galaxy Messier 5. an
incredible 28 million light years away. Called M51-ULS-1b, it was detected by
the conventional transit method but using X-ray observations rather than
visible light.
-
- The planet
orbits an X-ray binary system consisting of an ordinary sun-like star together
with a much more compact object such as a neutron star or black hole. These
systems are powerful emitters of X-rays, which is why they can be detected at
enormous distance.
-
- One of the
most recently discovered exoplanets, GJ 367 b, was announced in December, 2021
as one of the weirdest. Found using TESS, it's a small world, about half the
mass of Earth , and it’s so close to its parent star that it completes a whole
orbit in just 8 hours.
-
- In other
words, the planet’s "year" is just a third of an Earth day! At a
distance of 31 light years, GJ 367 b is close enough that astronomers can study
its properties in detail. They’ve worked out that it probably has a similar
composition to Mercury, and an even higher surface temperature up to 2,700
°F on the planet's dayside.
-
- Needless to
say that's far too hot for life to exist there, although it's possible there
are other more habitable planets orbiting further out from the same star.
-
- When GJ
1132 b was discovered by Chile's Cerro-Tololo observatory in 2015 it was hailed
as the closest Earth-size exoplanet known at that time. This made it
interesting enough to take a closer look with NASA’s own Hubble telescope.
Hubble was able to peer into the planet’s atmosphere, where it made a startling
discovery.
-
- Based on a
combination of observational evidence and computer modelling, scientists
believe it’s a "secondary" atmosphere formed by volcanic activity,
after radiation from the planet’s parent star destroyed its original atmosphere
. The new atmosphere isn’t a particularly hospitable one, though, consisting of
molecular hydrogen, cyanide, methane and an aerosol haze.
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March 2, 2023 EXOPLANETS - What
are some of them like?
3899
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--- Friday, March 3, 2023
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