![]() ![]() Also, dust in the system would dim their reflected light. This might be evidence for a third planet in the system.Īny inner planets would be difficult to detect because their light would be lost in the glare of the star. This larger disc has a curious gap at twice Pluto’s average distance from the Sun. The outer disc that the shadows are falling on may extend as far as several times the radius of our Solar System’s Kuiper belt. “ This is right in line with typical Solar System-style architecture,” said Debes. This is comparable to the range of orbital inclinations inside our Solar System. And the shadows complete one rotation around the star about every 15 years - the orbital period that would be expected at that distance from the star.Īlso, these two inner discs are inclined by about five to seven degrees relative to the plane of the outer disc. The suspected planets are located in a region roughly the distance of Jupiter from our Sun. It’s like two racing cars that are close to each other, but one slowly overtakes and laps the other,” said Debes. If one was moving much faster than the other, this would have been noticed in earlier observations. “ It does suggest that the two planets have to be fairly close to each other. Sometimes the labels will match up but then one gets ahead of the other. It’s sort of like spinning two vinyl records at slightly different speeds. The discs may be proxies for planets that are lapping each other as they whirl around the star. ![]() Hubble is piecing together a holistic view of the architecture of the system. The simplest explanation is that the misaligned discs are likely caused by the gravitational pull of two planets in slightly different orbital planes. It makes the system much more complex than we originally thought,” said Debes. ![]() “ We’ve never really seen this before on a protoplanetary disc. Over time they’ve now separated and split into two shadows. They were so close to each other in the earlier observation they were missed. The best solution the team came up with is that there are two misaligned discs casting shadows. “But to test this we had to run sophisticated models where we varied the number of discs and their orientations to try to reproduce Hubble’s observations.” “We hatched a theory of what might be causing the changing shadows,” added Rebecca Nealon, a member of the science team at the University of Warwick in the United Kingdom. I was flummoxed at first, and all my collaborators were like: what is going on? We really had to scratch our heads and it took us a while to actually figure out an explanation.” “ When I first looked at the data, I thought something had gone wrong with the observation because it wasn’t what I was expecting. “ We found out that the shadow had done something completely different,” said Debes, who is principal investigator and lead author of the study published in The Astrophysical Journal. John Debes of AURA/STScI for the European Space Agency at the Space Telescope Science Institute in Baltimore, Maryland, compared these latest observations of the TW Hydrae disc to Hubble observations made several years ago. The second shadow was discovered in observations obtained on 6 June 2021, as part of a multi-year programme designed to track the shadows in circumstellar discs. Because the TW Hydrae system is tilted nearly face-on as seen from Earth, it is an optimum target for getting a bird’s-eye view of a planetary construction yard. In its infancy, some 4.6 billion years ago, our Solar System may have resembled the TW Hydrae system. TW Hydrae is less than 10 million years old and resides about 200 light-years away. The two discs are likely evidence of a pair of planets under construction. This could be from yet another disc nestled inside the system. Now, a second shadow - playing a game of peek-a-boo - has emerged in just a few years between observations stored in the MAST archive of the NASA/ESA Hubble Space Telescope. One explanation is that an unseen planet’s gravity is pulling dust and gas into its inclined orbit. ![]() The shadow isn’t from a planet, but from an inner disc slightly inclined relative to the much larger outer disc - causing it to cast a shadow. In 2017 astronomers reported discovering a shadow sweeping across the face of a vast pancake-shaped disc of gas and dust surrounding the red dwarf star TW Hydrae. ![]()
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