Deserted exoplanet inexplicably survives host star’s death throes

In his search for giant stars that host large worlds, Samuel Grunblatt, an astrophysicist at Johns Hopkins University, came across a strangely bloated planet that is smaller, hotter and older than it is supposed to be. “We didn’t expect to find any planets that look like this,” he told Gizmodo.

The newly discovered planet had somehow withstood the intense radiation of its host star, creating a bloated atmosphere rather than being stripped to its core from being so close to such a massive star. The discovery suggests that Earth and the rest of the planets in our solar system may evolve differently as the Sun becomes a dying star. The new findings are detailed in a STUDY published on Wednesday at Astronomical Journal.

TIC365102760 b, also known as Phoenix, defies theories of how planets die. The exoplanet is classified as a hot Neptune, with its size somewhere between Neptune and Saturn. However, due to its proximity to its host star, the exoplanet has scorching hot temperatures compared to Neptune’s icy conditions. Phoenix completes an orbit around its host star every 4.2 days, and is about six times closer to its host star than Mercury is to the Sun. Its star is about three times larger in radius than our host star, causing exoplanet temperatures to reach 1,600 degrees Kelvin.

Orbiting so close to a massive star should have fried the exoplanet by now, but this big boy is here to stay. “Finding a planet that was actually the size of Neptune in such an intense environment was a surprise,” said Grunblatt, lead author of the study. “So then, our question became, how was this planet actually held in its atmosphere? And that’s something we’re still working on.”

Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), the scientists behind the new study developed their own pipeline for detecting giant stars. TESS is good at detecting low-density planets as they pass in front of their orbiting host stars, dimming the star’s brightness. The team filtered out unwanted light in the images taken by TESS and combined them with additional measurements from the WM Keck Observatory in Hawaii, which tracks tiny wobbles in stars caused by orbiting planets. In doing so, the researchers found a number of examples of giant star systems with large planets in their orbits.

Scientists behind the new study believe the exoplanet’s atmosphere was smaller when its host star was more similar to the Sun. However, as it aged and became a red giant star, the subsequent radiation may have caused the planet’s atmosphere to expand without losing it completely at that point.

Our Sun will approach its red giant stage about 6 billion years from now, running out of fuel and causing its core to contract. As it approaches death, the Sun will expand and engulf the inner planets of the solar system in the process (including Earth). This theory suggests that radiation from the dying Sun will have stripped the Earth of its atmosphere long before it was swallowed by its host star. The new discovery, however, suggests an alternative ending.

“What this is telling us is that, in fact, the atmosphere can last until that final stage where the planet is actually inside the star,” Grunblatt said. “It also has implications for all the evolutionary steps leading up to it.” For example, the presence of Earth’s atmosphere determines when water will permanently evaporate from all of the planet’s oceans. It also determines how long life can survive on Earth as the Sun reaches its final stages.

The bulge exoplanet is one of a series of “transiting giants” series, where researchers focus on finding exoplanets orbiting large stars. “We hope that by getting a larger population of transiting giants, we will then be able to … understand the evolution of the solar system in general.”

The team has applied to conduct follow-up observations of the newly discovered exoplanet using the Webb Space Telescope to be able to study its composition and retrace its history.

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