NASA's Hubble and New Horizons team up to keep an eye on Uranus together.

 

NASA's Hubble Space Telescope (left) and NASA's New Horizon's spacecraft (right) image the planet Uranus.

NASA's Hubble Space Telescope and New Horizons spacecraft recently targeted Uranus simultaneously, enabling scientists to directly compare the planet from two distinct perspectives. This collaboration provides valuable insights for future studies of similar exoplanets beyond our solar system.

Astronomers utilized Uranus as a representative model for these distant worlds, analyzing high-resolution images from Hubble alongside New Horizons' more remote observations. This dual perspective enhances scientists' understanding of what to expect when imaging exoplanets with upcoming telescopes.

"While we anticipated variations in Uranus's appearance across different observation filters, we were surprised to find that the planet was dimmer than expected in the New Horizons data," noted lead author Samantha Hasler from the Massachusetts Institute of Technology and a member of the New Horizons science team.

This image compares two three-dimensional shapes of Uranus (top) with actual views from NASA's Hubble Space Telescope (bottom left) and New Horizons (bottom right). Analyzing Hubble's high-resolution images alongside New Horizons' smaller perspective provides insights for future imaging of planets around other stars.

Direct imaging of exoplanets is crucial for assessing their potential habitability and offers insights into the origins of our solar system. Astronomers combine direct imaging and spectroscopy to analyze light from these distant planets, comparing brightness at various wavelengths. However, capturing images of exoplanets is challenging due to their vast distances, resulting in low-resolution pinpoints rather than detailed views like those of the planets in our solar system. Researchers can only directly image exoplanets during "partial phases," when a portion of the planet is illuminated by its star from our vantage point.

Uranus serves as an ideal test subject for understanding future observations of exoplanets. Many known exoplanets are gas giants similar to Uranus, and during the observations, New Horizons was positioned 6.5 billion miles away on the far side of Uranus, allowing it to capture the planet's twilight crescent—an angle unobservable from Earth. At this distance, New Horizons could only depict Uranus as a few pixels in its Multispectral Visible Imaging Camera.

In contrast, Hubble, situated in low-Earth orbit 1.7 billion miles from Uranus, captured detailed images of atmospheric features such as clouds and storms on the planet's day side. "Uranus appears as just a small dot in the New Horizons observations, akin to the dots seen in direct images of exoplanets from observatories like Webb or ground-based telescopes," said Hasler. "Hubble provides context for understanding the atmospheric dynamics at the same time."

The gas giants in our solar system exhibit dynamic atmospheres with changing cloud patterns. This raises questions about the variability of exoplanet atmospheres. By analyzing cloud details on Uranus captured by Hubble, researchers can confirm interpretations derived from New Horizons data. Notably, both observations revealed that Uranus's brightness remained consistent as it rotated, indicating stable cloud features.

The significance of New Horizons’ findings lies in its ability to observe how Uranus reflects light at a different phase than what Hubble or other Earth-based observatories can see. New Horizons suggested that exoplanets might be dimmer than anticipated at partial and high phase angles, revealing that atmospheric light reflection varies in these conditions.

NASA is developing two major observatories to further explore exoplanet atmospheres and assess potential habitability. "These landmark New Horizons studies of Uranus from a unique vantage point provide invaluable scientific knowledge and, like many other datasets obtained during the mission, offer surprising insights into the worlds of our solar system," said New Horizons principal investigator Alan Stern from the Southwest Research Institute.

This illustration depicts NASA's New Horizons spacecraft's view from deep in the Kuiper Belt, currently over 5 billion miles from Earth and 6.5 billion miles from Uranus. Researchers used Uranus as an exoplanet proxy, comparing Hubble's high-resolution images to New Horizons' smaller view to gain insights for future imaging of distant planets.

NASA's upcoming Nancy Grace Roman Space Telescope, launching by 2027, will employ a coronagraph to block starlight and directly observe gas giant exoplanets. Meanwhile, the Habitable Worlds Observatory, currently in early planning, will be the first telescope designed specifically to search for atmospheric biosignatures on Earth-sized rocky planets orbiting other stars."Studying how known benchmarks like Uranus appear in distant imaging can help us have more robust expectations for these future missions," concluded Hasler. "That will be critical to our success."

Launched in January 2006, New Horizons made a historic flyby of Pluto in July 2015 and provided humanity’s first close-up view of Kuiper Belt object Arrokoth in January 2019. Now in its second extended mission, New Horizons is studying distant Kuiper Belt objects and characterizing the outer heliosphere, making valuable astrophysical observations from its unique vantage point.The Uranus findings will be presented this week at the 56th annual meeting of the American Astronomical Society Division for Planetary Sciences in Boise, Idaho.

The Hubble Space Telescope, operational for over three decades, continues to make groundbreaking discoveries that enhance our understanding of the universe. A collaborative effort between NASA and the European Space Agency, Hubble is managed by NASA's Goddard Space Flight Center, with mission operations supported by Lockheed Martin Space. The Space Telescope Science Institute in Baltimore oversees Hubble’s science operations.

The Johns Hopkins Applied Physics Laboratory (APL) in Maryland built and operates the New Horizons spacecraft, managing the mission for NASA's Science Mission Directorate. The mission is directed by Southwest Research Institute under Principal Investigator Alan Stern and is part of NASA's New Frontiers program, managed by NASA's Marshall Space Flight Center.