Editorial Feature

Explaining The Latest CUTE Satellite Findings

The Colorado Ultraviolet Transit Experiment (CUTE) is a National Aeronautics and Space Administration (NASA) spacecraft. This cereal box-sized spacecraft observes large exoplanets in the near-ultraviolet (UV) region of the electromagnetic spectrum. This article provides an overview of CUTE and its new observations on ‘hot Jupiters’.

CUTE satellite, CUTE satellite findings, Colorado Ultraviolet Transit Experiment

Image Credit: FoxPictures/Shutterstock.com

Recent Developments in Space Observation

Telescopes and other instruments used to observe space have undergone significant developments over time. In the early 2010s, a new wave of observatories, larger than those built before the James Webb Space Telescope (JWST) and other high-tech UV/observation tools, was built both on the ground and in space.

Before the 2020 Decadal Survey on Astronomy and Astrophysics, scientific experts recommended that NASA build new observatories to increase the understanding of space in many areas. Simultaneously, smaller telescope arrays have also grown, and NASA has invested in smaller satellites covering various scientific fields.

A recent decadal survey highlighted the usefulness of small telescopes in space, such as CubeSats and smallsats, for observing sources for weeks or months. These small telescopes can help observe wavelengths that are otherwise not visible through ground telescopes. These observations complemented those made by the Hubble Space Telescope (HST), a space telescope that operates in a low Earth orbit.

What is CUTE?

Atmospheric escape plays a crucial role in shaping the composition, structure, and development of many planets. Various telescopic observations have shown that this process leaves detectable traces on exoplanets located close to their host stars and is primarily composed of gas. These signatures are caused by the intense extreme UV radiation emitted by the parent star.

An article published in The Astronomical Journal introduced the CUTE mission, which is NASA's first UV astronomy CubeSat and the first grant-funded small satellite dedicated to the characterization of extrasolar planetary atmospheres. This small satellite was designed to study the atmosphere of nearby planets by observing their transit across stars in the near-UV range.

CUTE aims to understand atmospheric escape and the composition of giant planet atmospheres by studying their near-UV spectra. It carries a special tool, a near-UV spectrograph connected to a telescope, to analyze the UV light. The data is captured using a special camera and stored on a UV-enhanced chip.

The CUTE spacecraft is approximately 14 inches long and was first launched in September 2021. Since then, it has aimed its telescope at a group of hot Jupiters, which are some of the hottest and largest planets in the galaxy, located several hundred years away from the Earth.

Similar to Jupiter, these gas giants orbit very close to their host stars, completing one rotation on just a few Earth days. Because of the intense radiation from their stars, hot Jupiters reach temperatures of thousands of degrees Fahrenheit, causing their atmospheres to greatly expand.

CUTE Observations on WASP-189b

WASP-189b is one of the hottest planets discovered to date, with a dayside temperature of about 3400 K, orbiting a bright A-type star. The exoplanet WASP-189b was initially targeted for CUTE's early science studies and was observed during three consecutive transits in March 2022. 

A recent article published in The Astrophysical Journal Letters reported the first near-UV observations of WASP-189b, acquired with the CUTE. Observations made by the CUTE instrument revealed that the near-UV transit depth was approximately three times that of the visual transit depth.

This transit depth suggested that the planet has a hot, extended upper atmosphere with a temperature of approximately 15,000 K. Using the most suitable model to explain the limits and temperature of the upper atmosphere, the overall mass-loss rate for all types of particles was determined to be 4 × 108 kg s−1.

At a resolution of 10 Å, the transmission spectrum of the planet revealed absorption by the Mg II lines beyond the Roche lobe at a significance level greater than 4σ. At a lower resolution of 100 Å, a quasi-continuous absorption signal was observed, which was in line with a "forest" of low-ionization metal absorption dominated by Fe II.

Interview Feature - CUTE: Characterizing Exoplanet Atmospheres with CubeSats

These findings suggest that the upper atmosphere of WASP-189b had a temperature of approximately 15,000 K, which is higher than that predicted by current state-of-the-art hydrodynamic models. The findings of this study on excess near-UV absorption in the planet were consistent with previous HST transit observations of similar exoplanets.

Drawbacks of CUTE

The initial two years of observations by CUTE on the planet yielded no fruitful results. However, unpublished findings revealed that the team had discovered a second planet, MASCARA-4b, which seemed to be losing very little gas. KELT-9b, on the other hand, fell somewhere in the middle.

Kevin France, the principal investigator for the CUTE mission, and his team hope that their findings on WASP-189b can shed light on why some planets lose significant portions of their atmosphere while others remain largely unchanged.

France believes that a combination of factors, such as the size of the planet (which generates a stronger gravitational pull) and the star’s dynamics (more active stars may cause more damage to planets than quieter stars), may be responsible for this phenomenon.


Overall,  the development of larger observatories on Earth and in space, as well as investments in smaller telescope arrays and satellites by NASA, have been driven by recent advancements in space observation. The significance of small telescopes in space for extended observations and the study of unique wavelengths has been highlighted, in addition to the work of the Hubble Space Telescope.

CUTE, a compact spacecraft from NASA, is the first UV astronomy CubeSat dedicated to studying the atmosphere of nearby planets by observing their transit across stars in the near-UV range.

Since its launch, CUTE has observed hot Jupiters and enormous planets orbiting very close to their stars. These planets experience extreme temperatures that cause their atmospheres to expand significantly, resembling dough rising in an oven.

CUTE's observations of WASP-189b, one of the hottest known planets, revealed an extended upper atmosphere with temperatures around 15,000 K, which is hotter than previously thought. The data showed significant near-UV absorption and revealed details about the composition and temperature of the upper atmosphere of the planet, deviating from existing models.

CUTE's work expands our knowledge of exoplanets and their atmospheres and offers insights into atmospheric escape and the diversity of planetary systems beyond our solar system.

References and Further Reading 

14-inch spacecraft delivers new details about ‘hot Jupiters’. Accessed on 20 December, 2021.

Sreejith, A. G et al. (2023). CUTE Reveals Escaping Metals in the Upper Atmosphere of the Ultrahot Jupiter WASP-189b. The Astrophysical Journal Letters, 954(1), L23. https://iopscience.iop.org/article/10.3847/2041-8213/acef1c/meta#apjlacef1cs5

France, K et al. (2023). The Colorado Ultraviolet Transit Experiment Mission Overview. The Astronomical Journal, 165(2), 63. https://iopscience.iop.org/article/10.3847/1538-3881/aca8a2/meta  

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Bhavna Kaveti

Written by

Bhavna Kaveti

Bhavna Kaveti is a science writer based in Hyderabad, India. She has a Masters in Pharmaceutical Chemistry from Vellore Institute of Technology, India, and a Ph.D. in Organic and Medicinal Chemistry from Universidad de Guanajuato, Mexico. Her research work involved designing and synthesizing heterocycle-based bioactive molecules, where she had exposure to both multistep and multicomponent synthesis. During her doctoral studies, she worked on synthesizing various linked and fused heterocycle-based peptidomimetic molecules that are anticipated to have a bioactive potential for further functionalization. While working on her thesis and research papers, she explored her passion for scientific writing and communications.


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