- 3864 - EXOPLANETS - so many discoveries? Astronomers have discovered more than 5,200 exoplanets, less than 200 are rocky terrestrial exoplanet. Exoplanet “Wolf 1069 b”, which orbits a red dwarf star, Wolf 1069, is only 31 light-years from Earth.
--------------------- 3864 - EXOPLANETS - so many discoveries?
- 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.
-
- It 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.
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- 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
discovery of Wolf 1069 b 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 telescope at the Calar Alto Observatory in
Spain.
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- 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”,
and “GJ 1002 b and c.”
-
- 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 as is
being currently undergone for transiting planets using JWST.
-
- 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. This isn't as easy as it
sounds, because distant planets are so faint they are usually lost in the
bright glare of their host stars. Nevertheless, 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. However,
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.
-
- In
practice, it's 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.
-
- 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.
-
- In the case
of “TIC 172900988 b”, the whole process was quick 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
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 have a planet orbiting around it. The brown
dwarf in question is “CFHTWIR-Oph 98”, and its planetary companion, possibly as
small as 4.1 Jupiter masses.
-
- The sun's
nearest cosmic neighbor is the red dwarf Proxima Centauri, a mere
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.
-
- Then in
2020, astronomers announced the likely discovery of a second planet in the same
system. However this one, dubbed Proxima Centauri c, is less likely to be
habitable, orbiting so far out that it receives very little of the star’s
warmth.
-
- TESS in
2020 discovered a family of four planets orbiting a sun-like star “HD 108236”.
Described by their discoverers 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, the super-Earth “HD 108236 b”. With 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, of
course, makes it too hot to inhabit. NASA estimates its surface temperature at
a scorching 1,500 degrees Fahrenheit.
-
- This huge
planet,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 the 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.
-
- By 2023, 120
exoplanets have been found by the gravitational microlensing technique. Many of
these bear the prefix OGLE, because they were detected by the “Optical
Gravitational Lensing Experiment”. One of the most recent discoveries,
OGLE-2019-BLG-0960 b, is particularly significant because it is the smallest
planet yet found by this method.
-
- It is
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.
-
-
“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, lurking in the
Whirlpool Galaxy Messier 5, an incredible 28 million light years away. “M51-ULS-1b”, was detected by the
conventional transit method but using X-ray observations rather than visible
light.
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- 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 distances.
-
- Exoplanets
“GJ 367 b”, announced in December 2021
is 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.
-
- It probably
has a similar composition to Mercury, and an even higher surface temperature up
to 2,700 °F on the planet's
dayside. 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.
-
February 6, 2023 EXOPLANETS - so
many discoveries? 3864
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--- Tuesday, February 7, 2023 ---------------------------
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