The Absolute Cosmos: A look into the atmosphere of a rare exoplanet that shouldn’t exist

Just 260 light years away, scientists discovered a rare hot Neptune exoplanet dubbed LTT 9779b last month, using NASA’s Transiting Exoplanet Survey Satellite (TESS) and Spitzer Space Telescope.

One of the main aim of TESS is to hunt for new small exoplanets that could be good targets for atmospheric characterisation. In the beginning of its mission, TESS found exoplanet LTT 9779b.

The exoplanet is orbiting a Sun like star in very close proximity and it is little larger than Neptune. It just takes nineteen hours to complete one orbit around its parent star.

LTT 9779b is located in hot Neptune desert, where planets are not thought to exist. What so strange about LTT 9779b is that despite being so close to its host star, the exoplanet still has considerable amount of atmosphere.

Scientists studied the infrared data of planet and its star collected by now retired Spitzer Space Telescope and published their findings in two studies.

In the first research a team of scientists headed by astronomer Ian Crossfield from the University of Kansas has explained the exoplanet’s temperature profile.

In second research a team headed by astronomer Diana Dragomir from the University of New Mexico has characterized the exoplanet’s atmosphere.

According to Crossfield, the exoplanet is subjected to so heavy amounts of radiation from its parent star that its temperature is over 1,650 degrees Celsius and its atmosphere could have evaporated completely.

Yet, the infrared observations from the Spitzer Space Telescope detected its atmosphere.

Since thermal energy is radiated in form of infrared radiation, this helps scientists in calculating the temperature of the objects located far away.

The system is placed so that when exoplanet passes between us and its host star, it provides us clean views of exoplanet’s both sides- the night side and day side.

This in turn allow scientists to calculate exoplanet’s temperature, as they can use the changing light of the whole system as the exoplanet orbits.

The hottest time of the day on exoplanet is in the noon at the time when Sun is directly overhead. Here on Earth hottest time of day is few hours after noon, this is because the heat enters our atmosphere faster than it is radiated back into the space.

According to scientists, the exoplanet is way too cooler than expected. This indicates that it reflects more of its starlight that it receives, which may be due to day side clouds.

Also, the exoplanet does not carry much heat to its night side. Scientists argue that this is because the star light absorbed is possibly in high atmosphere from where it is quickly radiated back into the space.

To further examine the exoplanet’s atmosphere, second team studied it via transit method.

According to team head Dragomir, exoplanet LTT 9779b is hard to explain as it doesn’t have enough mass to hold on its atmosphere for a very long time.

To solve this mystery team combined the secondary eclipse data from Spitzer Space Telescope with that of TESS data. The results returned with the evidence of carbon monoxide in exoplanet’s atmosphere.

Scientists don’t expect this from such a hot exoplanet. Carbon monoxide has been observed in hot Jupiters that also circle their stars at such close range.

But these hot Jupiters are more massive than hot Neptunes and they can retain their atmosphere by using their high gravity. It was believed that Neptune sized exoplanets should not be enough massive to do so.

Detecting carbon monoxide in hot Neptune’s atmosphere could throw light on planet’s formation and its atmosphere. Future observations will help us answer these questions.

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First paper:
Second paper:
