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The campaign was well underway when Bridges and Mandel joined. They found the lab when they were undergraduates, but their interest in astronomy was sparked much earlier. In elementary school, Bridges remembers bringing a stack of photos taken from the Mars Rover to show and tell. For Mandel, it was the recycled rockets SpaceX sent into space and then recovered that blew her away. The mentorship and hands-on experience they received convinced them to stay for their PhD. Colombia News spoke with Bridges and Mandel about studying Jupiter and the advice they have for other astronomy enthusiasts.
Q. What causes auroras?
Gabriel Bridges: Occur when charged particles from space strike a planet’s magnetic field and are deflected toward the planet’s north and south poles. The magnetic field attracts the particles, and when they crash into the atmosphere, they slow down considerably and emit a lot of electromagnetic radiation. On Earth, most radiation is visible light. If you are far enough north (or south), you will see brilliant green curtains of light that are the result of electrons colliding with oxygen atoms in our atmosphere.
Shifra Mandel: The magnetic field that connects the north and south poles of the Earth forms a protective barrier that prevents the solar wind from eroding our atmosphere; it also protects life from potentially harmful cosmic rays. The magnetosphere is constantly bombarded with charged particles; some penetrate the outer layers and are accelerated along the magnetic field lines towards the two poles. When these energetic particles collide with the Earth’s atmosphere, they generate auroras.
Q. What do the auroras look like from Jupiter?
GB: Interestingly, Jupiter’s aurora borealis is quite unimpressive, at least to the human eye. The real light show occurs at higher energies than what we can see. Jupiter’s ultraviolet auroras are bright, lingering features that can be seen in this visualization based on data from NASA’s Hubble Space Telescope. In this video, you can clearly see the magnetic fingerprint of Jupiter’s moon, Io. This luminous point at the bottom right of the aurora is the magnetic shadow of Io.
SM: Io is constantly bombarding Jupiter with charged particles from volcanic eruptions on its surface. These charged particles are the source of most of the X-ray emissions we see. In contrast, Earth’s main source of ions comes from periodic solar storms. Thus, our aurora borealis are not continuous like those of Jupiter.
Q. What’s so intriguing about Jupiter’s X-ray light?
GB: Jupiter’s magnetic field is 20 times stronger than Earth’s and the strongest in our solar system. If Jupiter’s magnetic field were visible at its widest point from Earth, it would appear three times larger than our sun or moon. This means that Jupiter has unparalleled power to accelerate and focus charged particles. Thus, you would expect more energetic X-rays from Jupiter than from Earth because its magnetic field generates such a large energetic acceleration.
Jupiter’s closest moon also emits a ton of ions and electrons every second. This gives Jupiter a constant supply of charged particles to power its auroras. Back on Earth, we have to wait for solar storms to pull charged particles into our atmosphere.
SM: If we were standing on Jupiter to observe Earth, we probably wouldn’t be able to see the Earth’s aurora borealis. But Jupiter’s auroras are so much more powerful that we can observe them from the same distance.
Q. What other planets in our solar system emit high energy radiation?
GB: The planets emit high-energy radiation through the auroras and by reflecting the X-rays emitted by the sun. To produce an aurora, three things are needed: a magnetic field, an atmosphere and a source of charged particles. Most planets in our solar system do not meet these criteria. Mercury has no atmosphere. Mars and Venus do not have a magnetic field. Uranus and Neptune have weak magnetic fields. That leaves Earth, Jupiter, and Saturn. We know Earth and Jupiter certainly have X-ray auroras, but we’re not sure about Saturn yet!
Q. What is the mystery at the heart of this article?
SM: The space probe Ulysses flew over Jupiter in 1992 equipped with a detector to record high-energy X-rays between 27 and 48 kiloelectronvolts (keV) but found nothing. This intrigued astrophysicists, who expected that electrons producing ultraviolet radiation from Jupiter’s auroras would also produce energetic X-rays. The mystery deepened when the European Space Agency’s XMM-Newton telescope later recorded high-energy X-rays near the upper end of its detection limit, around 7 keV. The source of this X-ray emission was unclear, but we were confident that NuSTAR, with its ability to detect radiation from 3 keV to 79 keV, could provide answers.
Q. How did you solve it?
SM: NuSTAR observations have confirmed that Jupiter produces X-rays as high as 20 keV – much higher than what XMM-Newton is able to detect, but below the detection band of Ulysses, which is why Ulysses missed it. To test our suspicions that the X-rays detected by NuSTAR were generated by electrons flowing through Jupiter’s atmosphere, we examined data from NASA’s Juno space probe; as Juno orbits Jupiter, it records the levels of charged particles in its path. We simulated the effects of these particles passing through and colliding with a Jupiter-like atmosphere. We found that the x-rays produced matched the radiation we saw with the NuSTAR telescope.
Q. What should everyone know about astrophysics?
GB: It’s not as pretentious and inaccessible as it may seem. Everyone can have an impact. All it takes is a lot of time and hard work. If you are interested, find a researcher and ask to work with him.
SM: It’s not easy, but if you like it, it’s really worth it!
Q. Any advice for other students debating a career in astronomy?
GB: I used to think that I couldn’t contribute to a research group until I knew X, Y and Z in physics. If you’re seriously interested, the best time to start researching is now. The second best time is tomorrow! You won’t know what a career in astrophysics is like until you try.
SM: Find your niche: something you’re passionate about, something that makes you want to get out of bed in the morning.
