Reducing Satellite Interference in Hubble Space Telescope Images
NGC 4676: Example of Satellite Trail in Hubble Space Telescope Exposure
Earth-Orbiting Objects Leave the Equivalent of "Scratch Marks" on Space Photos
Image Description: A large pair of colliding galaxies, sporting long tails of blue stars and gas emanating from each galaxy, is shown at the center of a primarily dark background. The trail of an artificial satellite is seen as the bright white band running across the top of the galaxies diagonally from the middle-left of the image towards the upper-right corner of the image. NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years distant, they have begun the process of colliding and merging.
When the Hubble Space Telescope was launched in 1990, there were about 470 artificial satellites orbiting Earth. By 2000, that number doubled. But by 2023, the rising number has grown almost exponentially to nearly 8,000 satellites. For Hubble this means that satellites photobomb about 10% of its exposures on celestial targets. However, a typical satellite trail is very thin and will affect less than 0.5% of a single Hubble exposure.
Nevertheless, these denizens leave annoying pencil-thin, white streaks across a Hubble image as they zoom overhead. And, they are not the only image artifacts Hubble astronomers have to contend with. Cosmic rays rain onto Hubble's camera detectors. These leave what looks like "scratch marks" too. In fact, they are a bigger nuisance than satellite trails.
Astronomers at the Space Telescope Science Institute in Baltimore, Maryland have developed tools for cleaning up this clutter. Hubble observations consist of more than just one exposure. And so, artifacts can be identified and subtracted between exposures because they are not in the same place on a detector.
It is estimated that by 2030 there could be ten times as many satellites circling Earth as there are now. Even as the number of satellites increases, the Space Telescope Science Institute's tools for cleaning the Hubble pictures will remain useful. To date not one Hubble science program has been affected by satellite trails.
Artificial satellites are photobombing the Hubble Space Telescope's snapshots as much as every two to four hours, according to researchers at Baltimore's Space Telescope Science Institute (STScI).
As they whirl around Earth, the satellites leave streaks across an image, like scratches on photographic film. Hubble is in a low-Earth orbit and so many satellites in higher orbits sweep overhead. As many as 8,000 satellites circle Earth—more than half for telecommunications.
But not to worry—experts say that they are not a threat to the celebrated telescope's ongoing observations of the universe.
"We developed a new tool to identify satellite trails that is an improvement over the previous satellite software because it is much more sensitive. So we think it will be better for identifying and removing satellite trails in Hubble images," said Dave Stark of STScI.
Stark applied the new tool, based on the image analysis technique known as the Radon Transform, to identify satellite trails across Hubble's camera with the widest field of view, the Advanced Camera for Surveys (ACS).
In 2002 the satellite streaks were present in five percent of ACS exposures, with many of those too faint to discern easily. This rose to ten percent by 2022, although the typical brightness of the detected trails remained unchanged.
As the number of artificial satellites encircling Earth rises, sky contamination for all telescopes based on the ground or in Earth orbit becomes increasingly worse.
"To date, these satellite trails have not had a significant impact on research with Hubble," said Tom Brown, Head of STScI's Hubble Mission Office. "The cosmic rays that strike the telescope's detectors are a bigger nuisance."
Previous studies regarding Hubble do not pick up the fainter satellite trails. The new software is up to ten times more sensitive than prior software developed by STScI to detect satellite trials, and it identifies roughly twice as many trails as other studies.
"We have a toolbox of things that people use to clean Hubble data and calibrate it. And our new application is another tool that will help us make the best out of every Hubble exposure," said Stark.
Read the full release:
https://www.stsci.edu/contents/media/images/2023/017/01H1Q4K5J650PPH3HM9Y88N7TA
Credit: NASA, European Space Agency (ESA), Space Telescope Science Institute (STScI)
Image Date: June 5, 2023
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