Hubble and New Horizons Look at Uranus at the Same Time

Ever since the advent of space exploration we have seen some amazing images of the planets. New technology often brings with it a new perspective and we have been reminded of this again just recently with images from the Hubble Space Telescope (HST)  and New Horizons spacecraft. The two objects simultaneously imaged Uranus from different perspectives in an attempt to predict what astronomers would see when they look at exoplanets orbiting other stars. 

Uranus is the 7th planet from the Sun and is recognisable for its wonderful blue-green colour. It was discovered by William Herschel in 1781 and since then we have been probing its secrets with telescopes and space probes alike. Like the other outermost planets, Uranus is a giant ball of gas and its the presence of methane in its atmosphere that gives it the striking colour. It’s unusual among the other planets since it seems to rotate around the Sun with an axial tilt of 98 degrees so it has really quite extreme seasons. 

This zoomed-in image of Uranus, captured by Webb’s Near-Infrared Camera (NIRCam) Feb. 6, 2023, reveals stunning views of the planet’s rings. Credit: NASA, ESA, CSA, STScI IMAGE PROCESSING: Joseph DePasquale (STScI).

HST and New Horizons have recently turned their gaze on Uranus but for a somewhat unusual project, to help develop imaging techniques for exoplanets. Directly imaging the distant alien worlds is tricky simply due to their distance and often due to their proximity to the host star. It’s of great importance to be able to study them directly to be able to learn more about their nature and possible habitability. Directly imaging exoplanets often just reveals pinpoints of light so researchers have used Uranus as a ‘proxy’ exoplanet to explore new imaging methods. 

The New Horizons instrument payload that is currently doing planetary science, heliospheric measurements, and astrophysical observations. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Uranus was chosen because the majority of exoplanets are gas giants and similar in nature. It was also chosen as New Horizons was on the far side of Uranus at the time of observation placing it 10.5 billion kilometres away. From its vantage point, New Horizons would see a crescent Uranus, a phase often seen on exoplanets when they are at their furthermost point from their star. They used the Multispectral Visible Imaging Camera to grab the images with Uranus covering just a few pixels, much like an exoplanet when viewed from Earth. 

While New Horizons was taking its images, HST which was just 2.7 billion km away and with its high quality cameras could capture a fabulous amount of detail in the atmosphere. By comparing the two images, the researchers have been able to see how atmospheric features appear in the New Horizon data to help learn about exoplanet observations. The team found that both HST and New Horizons saw that the brightness did not vary as the planet rotated which revealed that the cloud features were not changing with the rotation of the planet.

This image of NASA’s Hubble Space Telescope was taken on May 19, 2009 after deployment during Servicing Mission 4. NASA

They also found that New Horizons showed exoplanets are likely to seem dimmer than predicted at partial and high phase angles. This means that a gas planet like Uranus reflects light differently at partial phases when compared to others. The results are a testimony to the wonderfully insightful approach to cracking an existing challenge in modern astronomy; The direct study of exoplanets. Over the coming years telescopes like Nancy Grace Roman Space Telescope which is due for launch in 2027 has the ability to block out light to enable direct observations of exoplanets. This latest study will help to interpret the data revealed in future studies.

Source : NASA’s Hubble, New Horizons Team Up for a Simultaneous Look at Uranus

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