A small but powerful NASA spacecraft has collected valuable data on the atmospheres of exotic planets known as hot Jupiters. The findings, led by a team from CU Boulder, could help us understand how these worlds and others like them evolve over time.

What are hot Jupiters?

Hot Jupiters are gas giants similar to our own Jupiter in terms of mass and size, but with much higher temperatures. They orbit their stars so closely that a year can take just a few days. This short orbital distance exposes them to intense stellar radiation, which heats up and inflates their atmospheres.

Hot Jupiters were among the first and strangest planets to be discovered around other stars, and they challenge our theories of planet formation and evolution. Astronomers have found more than 700 of them so far in our galaxy, and they come in a variety of types and sizes.

How did CUTE study them?

CUTE stands for Colorado Ultraviolet Transit Experiment, a NASA CubeSat mission that launched in September 2021. It is a tiny spacecraft, measuring just 14 inches in length, but it carries a powerful ultraviolet telescope that can observe the light from distant stars as it passes through the atmospheres of their planets.

By analyzing the spectra of this light, CUTE can measure the chemical composition, temperature, and escape rate of the planetary atmospheres. CUTE is the first mission dedicated to studying hot Jupiters in the ultraviolet, which is a key wavelength to probe their atmospheric dynamics and evolution.

What did CUTE find?

The CUTE team, which includes several undergraduate and graduate students from CU Boulder, has observed seven hot Jupiters so far, with more on the way. Some of them seem to be losing their atmospheres, but others are not. The team also found that the planets can be grouped into three families, based on their temperature and atmospheric properties:

• The “cooler” hot Jupiters, with temperatures up to about 700 degrees Celsius (1,300 degrees Fahrenheit).
• The “hot” hot Jupiters, with temperatures from about 700 to 1,700 degrees Celsius (1,300 to 3,100 degrees Fahrenheit).
• The ultra-hot Jupiters, with temperatures above 1,700 degrees Celsius (3,100 degrees Fahrenheit).

The team also discovered some surprising features in the atmospheres of some of the planets, such as the presence of water vapor and carbon monoxide, which are not expected to survive at such high temperatures.

Why is this important?

The results from CUTE are important for several reasons. First, they provide new insights into the physical processes that shape the atmospheres of hot Jupiters and how they interact with their host stars. Second, they help us understand how these planets and others like them might have formed and evolved over time. Third, they demonstrate the potential of small and low-cost spacecraft to perform cutting-edge science in the field of exoplanet research.

The CUTE mission is also a precursor to future and more powerful missions that will study exoplanets in the ultraviolet and other wavelengths, such as the James Webb Space Telescope, which will launch in 2021, and the LUVOIR and HabEx missions, which are being proposed for the next decade. These missions will not only explore hot Jupiters, but also other types of planets, including those that could potentially harbor life.

The CUTE team presented their findings at the 2023 meeting of the American Geophysical Union in San Francisco, and they plan to publish them in a peer-reviewed journal soon.