Using the Hubble Space Telescope, scientists have discovered that a Jupiter-sized, cotton candy-like planet located about 350 light-years away is shrinking and may be on its way to becoming “sub-Neptune” or “super- Earth” world.
As well as being one of the lightest planets ever discovered, the extrasolar planet or ‘exoplanet’ called V1298 Tau b also happens to be one of the youngest worlds ever discovered as it crosses or ‘passes’ the face of its star.
V1298 Tau b orbits a star approximately 23 million years old, which is young compared to older stars such as our middle-aged star, the Sun, which is 4.6 billion years old. In this system it is accompanied by at least three other planets, V1298 Tau c, d and 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 across the face of its young parent star, classified as a T Taurus star, meaning it is a very young star with a mass similar to the Sun.
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“V1298 Tau b is about the size of Jupiter. However, we found that the mass of this planet is comparable 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 progenitor of Neptune or Sub-Neptune at this age.” Depending on the evolution of this planet, it could lose much of its primordial atmosphere and become a sub-Neptune or potentially even a super-Earth-like planet.”
Since the mass of Jupiter is roughly 20 times that of Neptune, the fact that V1298 Tau b is the width of the former with 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 found so far. Its density of 0.1 grams per cubic centimeter is comparable to cotton candy,” Barratt added.
Decoding the contracting atmosphere of V1298 Tau b
Using its transits, the team performed an atmospheric survey of V1298 Tau b and found a large and clear atmosphere extending about 621 miles (1,000 kilometers). This is much wider than the atmospheres of Solar System bodies such as Saturn’s largest moon Titan, which have atmospheres that extend from their main body by between 31 miles and 62 miles (50 to 100 kilometers).
V1298 Tau b is only about 16 million miles from its highly active, hot young parent star T Taurus, 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 destroys its atmosphere.
The team also found that the interior of this planet is very hot, although it is expected to cool as it matures, which also contributes to the loss of atmosphere.
“The combination of these processes is likely to result in significant mass loss and contraction of this planet,” Barratt said. “A comparison of the nature and composition of V1298 Tau b with mature sub-Neptunes highlights significant differences. It is therefore possible that during its evolution the atmospheric composition and chemistry of V1298 Tau b will also change.’
As a result, V1298 Tau b tells astronomers that when Neptune and sub-Neptune are first born in a cloud of gas and dust surrounding a young star called a “protoplanetary disk,” they are in a state unlike the , on which mature ages appear. The research also suggests that Neptune and sub-Neptune planets can change positions in their planetary systems.
“They are born with significantly large primordial envelopes that were likely accreted as they formed within a protoplanetary disk,” Barratt said. “By analyzing the atmospheric content of V1298 Tau b, we believe that this planet may have formed near 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 across the face of its star using a process called spectroscopy can reveal its composition.
For V1298 Tau b, this study revealed something unusual about the atmosphere of this exoplanet. It is surprisingly low in “metals,” which is the term astronomers use for elements that are heavier than the two lightest elements in the universe, hydrogen and helium.
“We were surprised not to find methane. The temperature of this planet is perfect for producing a large amount of methane,” Barratt said. “However, its absence points to chemical processes in the atmosphere, such as strong vertical mixing, that could remove methane from the observed atmosphere.”
The scientist from the University of Amsterdam explained that methane can only be removed if the interior of the planet is very hot. The lack of methane in V1298 Tau b’s atmosphere led them to suggest that temperatures in the planet’s atmosphere were 80 degrees Fahrenheit (27 degrees Celsius) or more. By comparison, the average temperature of Jupiter’s atmosphere is minus 166 degrees Fahrenheit (minus 110 degrees Celsius).
Barratt said the current observations only observe water vapor in V1298 Tau b’s atmosphere. 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 list of chemicals present in this exoplanet’s atmosphere.
“It is important to precisely constrain these abundances because they are directly related to the location of the formation of this planet,” Barratt added. “It is also important to study the impact of the host star on the planet’s atmospheric chemistry.”
Barratt and colleagues obtained observations of V1298 Tau b with 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 answer these questions,” Barratt concluded.
The team’s research was published May 9 in the journal Nature Astronomy.
