The world of exoplanets is definitely fascinating. HD 63433 is a Sun-like star about 75 light-years from Earth that was already known to host several gas giant-type exoplanets. But data from the Tess satellite now suggests that this star is also orbited by a young rocky planet that is almost the size of Earth but has half a global ocean of lava.
On Earth, lava lakes are a dream, generally ephemeral, a minority can persist for at least centuries, with activity waning at times. The best known in this regard are those of Nyiragongo in the Democratic Republic of Congo and the lava lake of the Kilauea volcano in Hawaii, which cyclically empties and fills. Without forgetting, of course, that of Erta Alé in Ethiopia.
We have known for several years about a planetary system discovered around the star, numbered HD 63433 in the famous Henry Draper Catalog (HD). It is about 0.91 times as large and 0.99 times as massive as the Sun, making it a G2 star. But a team of astronomers using NASA's Transiting Exoplanet Survey Satellite (Tess) space telescope has just announced that a new exoplanet has formed there, in a paper freely available on arXiv. Proofs. This time it is not a gas giant, but a rocky planet with a mass and size comparable to Earth (about 1.1 times its radius).
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The Henry Draper (HD) catalog brings together data on more than 225,000 stars with apparent magnitudes up to about 9. Founded in the early 20th century by astronomer Annie Jump Cannon and her colleagues at Harvard College Observatory, it covers almost the entire celestial vault away. The name goes back to a pioneer of astrophotography who was the first to obtain a star spectrum, that of Vega, in 1872. At his death, his widow had financed the creation of this catalog, which later became widely used by astronomers. For this reason, several stars in the Milky Way that have been studied for their exoplanets are designated by the letters HD.
https://www.youtube.com/watch?v=_2th8dY03Where
First one-minute video from the Actsafe expedition to Nyiragongo Volcano in February 2016, uploaded in Goma, Democratic Republic of Congo, Africa. © geoffmackley
A synchronously rotating exoplanet with a hot lave over 1,200 °C?
But that's where the comparison ends: HD 63433 d completes its orbit around the sun in just 4.2 days. Mercury still takes 88 days and its surface temperature averages around 167°C. It is therefore not surprising to learn that this planet, discovered by the method of planetary transit and in synchronous rotation, is the star HD 63433, also called TOI 1726 (TOI stands for Tess Object of Interest, in English). The surface temperature of its daily hemisphere, which is constantly facing the sun, is so high that the rock has to melt. It is estimated at 1,257°C. As a reminder: On Earth, lava temperatures vary depending on chemical composition between 500 °C (for example, the natrocarbonatites of Ol Doinyo Lengai reach 540 to 593 °C) to 1,200 °C (basalt is only liquid at more than 1,100 °C). °C).
HD 63433 d is notable in other respects and not only because it is therefore very likely that its diurnal hemisphere is a global lava ocean. It is the smallest confirmed exoplanet, less than 500 million years old. It is also the closest Earth-sized planet to this young planet and is about 400 million years old.
Finally, as explained in a NASA press release, the scorching temperatures on HD 63433 d are comparable to those of lava worlds such as CoRoT-7 b and Kepler-10 b.