Using the Hubble Space Telescope, scientists have discovered that a cotton candy-sized Jupiter-like planet about 350 light-years away is shrinking and could be on its way to “sub-Neptune” or “super-Earth” size. world.
In addition to being one of the lightest planets ever discovered, the extrasolar planet, or “exoplanet,” called V1298 Tau b is also one of the youngest worlds ever discovered as it crosses, or “transits,” the face of its star.
V1298 Tau b orbits a roughly 23-million-year-old star that is young compared to older stars such as our middle-aged star, the Sun, which is 4.6 billion years old. It is accompanied in this system by at least three other planets, V1298 Tau c, da e. This means that this system offers astronomers a unique opportunity to study the atmospheres of newly formed and developing planets.
To do this, the team used the Hubble Wide Field Camera 3 (WFC3) instrument to observe V1298 Tau b as it passes the face of its young parent star, classified as a T Tauri star, meaning it is a very young star with a mass similar to the Sun.
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“V1298 Tau b is the size of Jupiter. However, we found that the mass of this planet is comparable to or even lower than that of Neptune,” research team leader Saugata Barat of the University of Amsterdam told Space.com. “Therefore, it is likely to be a Neptune or Sub-Neptune progenitor at this age. Depending on the evolution of this planet, it could lose a large chunk of its primordial atmosphere and end up as a sub-Neptune or potentially even a super-Earth-like planet.”
Since Jupiter is about 20 times the mass of Neptune, the fact that V1298 Tau b is the width of the former and the mass of the latter means that this exoplanet is incredibly “bloated” as astronomers currently see it.
“V1298 Tau b is one of the lowest-density planets we’ve discovered so far. Its density of 0.1 grams per cubic centimeter is comparable to cotton candy,” Barat added.
Decoding the shrinking atmosphere of V1298 Tau b
Using its transits, the team conducted an atmospheric survey of V1298 Tau ba and discovered a large and clear atmosphere extending for about 621 miles (1,000 kilometers). This is much wider than the atmospheres of Solar System bodies such as Saturn’s largest moon Titan, whose atmospheres extend 50 to 100 kilometers from their main body.
V1298 Tau b is only about 16 million miles from its highly active, hot, young parent star T Tauri, meaning it completes an orbit in just 24 Earth days. As a result of this proximity, the planet is also bombarded with high doses of ultraviolet and X-ray radiation from its star, which strips away its atmosphere.
In addition, the team found that the interior of this planet is very hot, although it is expected to cool during maturation, which also contributes to the loss of atmosphere.
“The combination of these processes is likely to lead to significant mass loss and contraction of this planet,” Barat said. “Comparisons between the nature and composition of V1298 Tau b with mature sub-Neptunes highlight significant differences. Therefore, it is possible that during its evolution, the composition and chemistry of V1298 Tau b’s atmosphere may also change.”
As a result, V1298 Taub tells astronomers that when Neptunes and sub-Neptunes are first born in a cloud of gas and dust surrounding a young star called a “protoplanetary disk,” they are in a state unlike what they appear as adults. Research also suggests that Neptune and the Neptune subclass planets can change positions in their planetary systems.
“They are born with significantly large primordial envelopes that probably formed when they were forming in the protoplanetary disk,” Barat said. “Based on an analysis of the atmospheric content of V1298 Tau b, we think that this planet may have formed close to its current location near its host star.”
Because elements and chemical compounds absorb and emit light at characteristic wavelengths, analyzing the light that passes through a planet’s atmosphere as it passes the face of its star, using a process called spectroscopy, can reveal its composition.
For V1298 Tau b, this investigation revealed something unusual about the exoplanet’s atmosphere. It is surprisingly low in “metals,” the term astronomers use for elements heavier than the two lightest elements in the universe, hydrogen and helium.
“We were surprised not to detect methane. The temperature of this planet is ideal for producing large amounts of methane,” Barat said. “However, its absence points to chemical processes in its atmosphere, such as strong vertical mixing, which can remove methane from the observable atmosphere.
The scientist from the University of Amsterdam further explained that methane can only be removed if the interior of the planet is very hot. The missing methane in V1298 Tau b’s atmosphere led them to hypothesize that temperatures in the planet’s atmosphere are 80 degrees Fahrenheit (27 degrees Celsius) or higher. By comparison, the average temperature of Jupiter’s atmosphere is minus 166 degrees Fahrenheit (minus 110 degrees Celsius).
Barat said that the current observations have only observed water vapor in the atmosphere of V1298 Tau b. This means that in the future they intend to measure the abundance of other molecules such as carbon dioxide, carbon monoxide and sulfur dioxide to complete the inventory of chemicals present in this exoplanet’s atmosphere.
“It is important to precisely constrain this amount because it is directly related to the place of formation of this planet,” Barat added. “It is also important to investigate the impact of the host star on the chemistry of the planet’s atmosphere.”
Barat and colleagues obtained an observation of V1298 Tau b using the James Webb Space Telescope (JWST), which they are currently analyzing.
“JWST is sensitive to a wide range of molecules such as water, methane, carbon dioxide, carbon monoxide and sulfur dioxide. So we will soon be able to address these questions,” concluded Barat.
The team’s research was published May 9 in the journal Nature Astronomy.