00:01Look at this fascinating planet.
00:03It looks like a prey to flames.
00:05Its surface must be even more burning than the heart of the Valley of Death.
00:09The ground, arid and cracked by huge cracks,
00:13shows an absolute dryness.
00:17Not a single drop of water exists in this overheated universe.
00:20Yet, here is the same planet under a completely different face.
00:23Now, it is plunged into a glacial cold.
00:27The temperatures there are so low that any form of life would be strictly impossible.
00:33This singular world, called HD 2794D,
00:37is located at 19.7 light years from Earth,
00:41within the constellation of Eridan.
00:43It is a super-Earth,
00:45that is to say, a planet more massive than Earth,
00:48but more modest than glacial giants like Neptune.
00:51What distinguishes it is its atypical orbit,
00:54which sometimes makes it penetrate, sometimes leaves the habitable zone of its star.
00:59This region, where the conditions of temperature
01:01could allow the presence of water in liquid form.
01:05However, this intriguing planet has never been observed directly.
01:09Astronomers detected it by analyzing tiny oscillations of its star,
01:14thanks to two high-precision instruments,
01:16ESPRESSO and HAPS,
01:18installed on telescopes in Chile.
01:20These tools measure radial speed,
01:23that is to say, the slight movements of the star caused by the gravitational attraction of the planet.
01:28The more this oscillation is marked,
01:30the more the planet that is at the origin of it is massive.
01:35By exploiting these data,
01:36researchers have determined that this planet had a mass about 6 times higher than that of Earth.
01:42It gravitates around a star, HD 2794,
01:47also known as 82G.
01:50Eridani, slightly smaller and less luminous than our sun.
01:54What makes it unique is that it is bright enough to be visible to the naked eye,
02:00unlike many other stars housing exoplanets,
02:04that it is impossible to see without a telescope.
02:07This system has been under surveillance for more than 20 years.
02:11For a long time.
02:12Scientists suspected that it sheltered several planets,
02:15and in 2011, they confirmed the presence of two super-Earths,
02:19HD 2794D and HD 2794C,
02:24respectively making a revolution around the star in 18.3 and 89.6 days.
02:32For a while, a third planet,
02:34whose orbital period was estimated at 40 days,
02:37seemed to have been detected.
02:39Researchers began to doubt it,
02:41but after the thorough re-evaluation of several years of data,
02:45they ended up validating its existence.
02:47This is the extreme HD 2794D.
02:54Michael Kretinier, a researcher at the University of Oxford,
02:57played a decisive role in identifying this planet.
03:01He relied on an IT algorithm called Yarrara
03:05to isolate the low signal of the planet from the background noise.
03:08Thanks to this method,
03:10he was able to confirm not only the existence of HD 2794D,
03:16but also its exceptional character.
03:18Unlike the planets of our solar system,
03:21which follow essentially circular trajectories,
03:24this one adopts a strongly elliptical and elongated orbit.
03:29It takes 647 days to complete a revolution around its star,
03:34which is 40 days less than the duration of the Martian orbit around the Sun.
03:38At its apex, this planet is at a distance
03:41equivalent to twice the Earth-Sun interval,
03:43placing it well beyond the habitable zone.
03:46But at its perigee, it approaches up to 0.75 UA,
03:51penetrating then into the region
03:53where temperatures could allow the presence of liquid water.
03:56This extreme oscillation generates strange seasons.
04:00During a part of its orbit,
04:02HD 2794D turns into a real desert of ice.
04:08As the planet approaches its star,
04:10temperatures rise,
04:12and the ice must then melt,
04:14giving birth to ephemeral oceans.
04:16It thus goes through a brief period of torrid heat,
04:19so intense that water on the surface could evaporate into the atmosphere.
04:23But as soon as the planet moves away,
04:25a misty autumn sets in, accompanied by rain,
04:28before giving way to a harsh winter.
04:32In other words, this planet is also between extreme cold and overwhelming heat,
04:37making its environment unpredictable for any form of life.
04:41If organisms have developed there,
04:43they must necessarily be able to resist an environment in perpetual upheaval.
04:48But why is HD 2794D such a singular orbit?
04:54It could be the remains of events that occurred billions of years ago,
04:58while the planetary system was still in formation.
05:02At a later time,
05:04another planet of size could have disturbed its orbit,
05:07imposing this trajectory on it.
05:09Another theory suggests that a giant planet once present in the system
05:13would have forced HD 2794D to follow an elongated orbit
05:18under the effect of its gravitational influence.
05:21Later, this giant could have been expelled from the system,
05:25abandoning HD 2794D on its current trajectory.
05:30This theory seems coherent,
05:32because the two other planets in the system,
05:34HD 2794B and HD 2794C,
05:39evolve on much more regular orbits.
05:42The discovery of this planet is fascinating,
05:45because it questions our understanding of living worlds.
05:49Unlike the planets that permanently reside in the habitable zone,
05:53HD 2794D only crosses it.
05:57Scientists want to know if it could still shelter life,
06:01if only temporarily.
06:03To answer this question,
06:05future telescopes will analyze its atmosphere
06:07in search of water, gas, or even biological traces.
06:13Another super-Earth likely to shelter life
06:15evolves around a star located 137 light-years away.
06:19In astronomical terms, it is relatively close.
06:22A light-year is equivalent to about 9.5 billion kilometers.
06:26Named Toei 515b,
06:28this planet is once and a half larger than Earth,
06:31and, unlike HD 2794D,
06:35it remains permanently in the habitable zone.
06:38Look, here's what astronomers think this planet could look like.
06:43Toei 515b loops its orbit very quickly,
06:46in just 19 days.
06:48But although it is close to its star,
06:50it could not be excessively hot,
06:52because its star is a red dwarf,
06:55a celestial body smaller and colder than our sun.
06:58This means that Toei 515b could have a warmer climate
07:02than other exoplanets orbiting warmer stars.
07:07NASA detected this planet
07:09thanks to the Satellite Transiting Exoplanet Survey,
07:12which detects exoplanets by observing
07:14the slight decrease in brightness of a star
07:16when a planet passes in front of it.
07:18As red dwarfs are smaller and less bright than the sun,
07:22transiting planets are easier to identify.
07:26Astronomers plan to study this planet
07:28through the James Webb Space Telescope.
07:32Located 1.6 million kilometers from Earth,
07:35this ultra-performing telescope
07:37is able to analyze the atmosphere of exoplanets.
07:40If Toei 515b has one,
07:43it could help researchers identify the gases present
07:46and evaluate whether the conditions are conducive to liquid water,
07:49or even to life.
07:52Another promising world in our extraterrestrial life quest
07:55is an ultra-dense super-Earth of the K2-360 system.
07:59An international team of Japanese and European researchers
08:02identified this planetary system in orbit
08:04around a star similar to the sun,
08:06750 light years away.
08:08This system contains two planets,
08:10including one of the densest rock exoplanets ever discovered.
08:14K2-360b is a rock super-Earth,
08:17measuring about 1.6 times the size of Earth,
08:21but with a mass 7.7 times greater,
08:24which makes it as dense as lead.
08:26It orbits around its star at lightning speed,
08:30completing a revolution in just 21 hours.
08:33It is the planet known for its densest ultra-short revolution period,
08:37with well-measured properties.
08:39Its neighbor, K2-360c,
08:42is a much more massive planet,
08:44with at least 15 Earth masses.
08:46It takes 9.8 days to orbit,
08:48but as it does not pass in front of its star from our point of view,
08:51its exact size remains unknown.
08:55This exceptionally dense planet
08:57could be the residual core of a much larger star.
09:01The intense radiation of its star
09:03could have, over time,
09:05blown its external layers,
09:07leaving only a rocky core.
09:09It could thus offer a glimpse of the fate of planets
09:12too close to their star.
09:14Astronomers estimate that K2-360b
09:16could have migrated inland
09:18as a result of gravitational interactions
09:20with its more massive companion.
09:22One of the hypotheses is based on a high eccentricity migration,
09:26where the initially stretched orbit of the planet
09:29gradually stabilizes,
09:31making it more circular near the star.
09:33Another theory suggests that the rotation
09:35and axial inclination of the planet
09:37could play a role in this phenomenon.
09:39Planets of this type are rare,
09:41and discovering a combination of a giant companion
09:44would allow to refine the models of scientists
09:46on the formation and planetary evolution
09:49in extreme environments.
09:51This discovery could also enlighten
09:53the future of rocky planets,
09:55in particular those that are too close to their stars.
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