00:00Look at this fascinating planet.
00:03It looks as if it's burning.
00:05It must be hotter on its surface than in the middle of Death Valley.
00:09The ground is parched, cut by giant cracks.
00:13There's not a drop of water in this boiling world.
00:17Now it's the same planet, but it looks like a totally different place.
00:22Everything is frozen.
00:23The temperatures are so low, there isn't even a tiniest chance that life could survive
00:27on this planet.
00:30This bizarre world is called HD 20794 d, and it's located 19.7 light-years away from Earth,
00:38in the constellation Eridanus.
00:41This planet is a super-Earth.
00:43This term means that it is larger than Earth, but smaller than such ice giants as Neptune.
00:50What makes this planet especially interesting is its unusual orbit, which moves it in and
00:55out of its star's habitable zone.
00:57The region where temperatures might allow liquid water to exist.
01:02Now we haven't seen this unusual planet directly.
01:06Astronomers detected it by measuring tiny wobbles in its star using two powerful instruments,
01:11ESPRESSO and HARPS, located at telescopes in Chile.
01:17These instruments measure radial velocity, which is the small movement a star makes as
01:22a planet's gravity tugs on it.
01:24The larger the wobble, the more massive the planet.
01:28Later, astronomers analyzed the data and figured out that the planet in question has a mass
01:33around six times greater than Earth's.
01:36It orbits a star, which is slightly smaller and dimmer than our sun.
01:42What makes this star unique is that it is bright enough to be seen with the unaided
01:46eye, unlike many other stars that host exoplanets.
01:50You won't be able to see them without a telescope.
01:53The star system has been observed for over 20 years.
01:57Astronomers have long suspected it had multiple planets.
02:01In 2011, scientists discovered two other super-Earths orbiting the star every 18.3 and 89.6 days
02:10respectively.
02:12For some time, researchers thought they had found a third planet with an orbital period
02:17of 40 days.
02:18Later, they realized they had made a mistake.
02:22More recently, after reanalyzing years of data, astronomers have confirmed that the
02:27third planet does exist, and it's our extreme HD 20794d.
02:34A researcher from the University of Oxford played a key role in identifying the planet.
02:41He used a special computer algorithm called Yorara to separate the planet's weak signal
02:46from the background noise.
02:48It helped him confirm that the planet truly existed, and was pretty unique.
02:54Unlike the planets in our solar system, which have mostly circular orbits, the newly discovered
02:59one follows a highly elliptical, stretched-out orbit.
03:03It takes 647 days to complete one trip around its star.
03:08That's just 40 days shorter than Mars' orbit around the Sun.
03:13At its furthest point, the planet is twice the Earth-Sun distance, which makes it an
03:18icy world far outside the habitable zone.
03:22At its closest point, it moves inward to .75 AU, where it enters the habitable zone where
03:28liquid water might exist.
03:31This extreme movement creates truly bizarre seasons.
03:35For some part of its orbit, HD 20794d is frozen like an icy wasteland.
03:42As it approaches its star, temperatures rise and ice likely melts, forming temporary oceans.
03:49The planet then experiences a short, scorching summer.
03:53It is so hot that the water on its surface might evaporate into the atmosphere.
03:59Shortly after, the planet moves away again.
04:02It triggers a gloomy fall with rains, followed by a deep freeze in winter.
04:08In other words, the planet switches between extreme cold and intense heat, which makes
04:13it a very unpredictable place for life.
04:17If any lifeforms exist there, they certainly need to adapt to dramatic changes in temperature
04:22and environment.
04:25Why does the planet follow such a mind-boggling orbit?
04:29It might be a leftover effect from events billions of years ago, when the planetary
04:33system was still forming.
04:36At some point, another large planet may have disturbed the orbit of our extraordinary friend.
04:43Another possible explanation is that a giant planet once existed in the system, and its
04:48gravity pushed HD 20794d into an elongated path.
04:54Later, this giant planet may have been ejected from the system, leaving the smaller planet
04:59in its current orbit.
05:02This theory makes sense because the two other planets in the system, B and C, have more
05:06normal circular orbits.
05:09The discovery of this planet is so exciting because it challenges what we know about habitable
05:15planets.
05:16Most planets in the habitable zone stay there permanently, but HD 20794d only passes through
05:23it.
05:25Scientists want to know if such a planet could still support life, even briefly.
05:30So future telescopes will study the atmosphere of this planet looking for signs of water,
05:35gases, or even life.
05:38Another super-Earth that might have the right conditions for life orbits a star 137 light-years
05:44away.
05:46In space terms, this is considered relatively close.
05:50A light-year is around 6 trillion miles.
05:53The planet is called TOI-715b, and it's about 1.5 times the size of Earth.
06:01Unlike HD 20794d, it's permanently located in the habitable zone.
06:07Look, that's what astronomers think the planet might look like.
06:12TOI-715b orbits its star very quickly, completing a full orbit in just 19 days.
06:20But even though it's close to its star, it may not be extremely hot, all because its
06:26star is a red dwarf.
06:29That's a type of star that is smaller and cooler than our sun.
06:33This means TOI-715b could have a milder temperature compared to other exoplanets that orbit closer
06:41to hotter stars.
06:44NASA discovered the planet using the Transiting Exoplanet Survey Satellite.
06:49This space telescope finds planets by watching for small dips in a star's brightness, which
06:54happen when a planet passes in front of it.
06:58Since red dwarfs are smaller and dimmer than the sun, planets passing in front of them
07:02are easier to detect.
07:06Astronomers are planning to study the planet further using the James Webb Space Telescope.
07:12This powerful telescope, located 1 million miles away from Earth, can analyze the atmospheres
07:18of distant planets.
07:21If TOI-715b has an atmosphere, JWST could help scientists determine what gases are present
07:29in it and whether such conditions could support liquid water or even life.
07:36One more promising world for our search for extraterrestrial life is an extremely dense
07:41super-Earth in the K2-360 system.
07:46An international team of researchers from Japan and Europe has discovered this remarkable
07:51multi-planet system orbiting a sun-like star, located 750 light-years away.
07:58This system has two planets, including one of the densest rocky planets ever found.
08:05The K2-360b is a rocky super-Earth, about 1.6 times the size of Earth but with a mass
08:117.7 times greater.
08:14This makes it as dense as lead.
08:18The planet orbits its star incredibly fast, completing one full orbit in just 21 hours.
08:25It's the densest known ultra-short-period planet with well-measured properties.
08:30As for its sibling, this is a much larger outer planet with at least 15 Earth masses.
08:37It takes 9.8 days to orbit its star.
08:41Sadly, since it does not pass in front of its star from our viewpoint, scientists cannot
08:46determine its exact size.
08:50The unusually dense planet might be the core of a much larger planet.
08:54Over time, intense radiation from its parent star may have blown away its outer layers,
09:00leaving behind only its dense, rocky core.
09:03So, in fact, this planet could show us what might happen to some planets that are too
09:09close to their stars.
09:12Astronomers think that the planet may have moved inward over time due to interactions
09:16with its larger companion planet.
09:19One possibility is high eccentricity migration, where a planet's orbit becomes highly stretched
09:25out due to gravitational interactions before gradually becoming more circular near the
09:30star.
09:32Another theory is that the planet's spin and axial tilt can cause its orbit to become
09:37more circular.
09:39Such planets are rare, and finding one with a massive outer companion can help scientists
09:44refine their theories about how planets form and evolve in extreme environments.
09:50With its help, we might also understand how rocky planets evolve, and what happens to
09:55planets that get too close to their stars.
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