Dark birthplace could explain Jupiter’s strange chemistry


Jupiter may have formed in a shadow that kept the planet’s birthplace cooler than Pluto. The freezing temperature could explain the unusual abundance of certain gases in the giant world, suggests a new study.

Jupiter is composed primarily of hydrogen and helium, which were the most common elements in the planetary spawning disc that revolved around the newborn sun. Other elements that were gases near Jupiter’s birthplace also became part of the planet, but only in the same proportions as they existed in the protoplanetary disc (ND: 06/12/17).

Astronomers believe that the composition of the sun’s elements largely mirrors that of the protoplanetary disk, so Jupiter’s should look like this solar composition – at least for elements that were gases. But nitrogen, argon, krypton, and xenon are about three times more common on Jupiter, compared to hydrogen, than on the sun.

“This is the main puzzle in Jupiter’s atmosphere,” explains Kazumasa Ohno, a planetologist at the University of California at Santa Cruz. Where do these additional elements come from?

If Jupiter had been born at its current distance from the sun, the temperature at the planet’s birthplace would have been around 60 Kelvin, or -213Ëš Celsius. In the protoplanetary disk, these elements should be gases at this temperature. But they would freeze below about 30 kelvins, or -243 – C. It is easier for a planet to accrete solids than gases. So if Jupiter somehow appeared in an environment much colder than its current focus, the planet could have acquired solid objects loaded with these extra elements in the form of ice.

For this reason, in 2019, two different research teams independently suggested that Jupiter originated in the deep frost. beyond the current orbits of Neptune and Pluto, then spiraling inward towards the sun.

Ohno and astronomer Takahiro Ueda of the National Astronomical Observatory of Japan come up with a different idea: Jupiter formed where it is, but a clump of dust between the planet’s orbit and the sun blocked the light. of the sun, casting a long shadow that cooled Jupiter’s birthplace. The freezing temperature caused nitrogen, argon, krypton and xenon to freeze and become a bigger part of the planet, suggest scientists in a study in July Astronomy & Astrophysics.

The dust that cast the shadow came from rock objects closer to the sun which collided and shattered. Further from the sun, where the protoplanetary disk was colder, the water froze, giving rise to objects that looked like snowballs. When these snowballs collided, they were more likely to stick together than shatter and therefore didn’t provide much shade, the researchers said.

“I think it’s a smart solution to something that might have been difficult to rectify otherwise,” says Alex Cridland, an astrophysicist at the Max Planck Institute for Alien Physics in Garching, Germany.

Cridland was one of the scientists who had suggested that Jupiter had formed beyond Neptune and Pluto. But this theory, he says, means that Jupiter must have come much closer to the sun after birth. The new scenario avoids this complication.

the planet saturn
Measuring Saturn’s atmospheric composition can locate Jupiter’s birthplace.NASA, ESA, A. Simon / GSFC, MH Wong / UCB, the OPAL team

How to test the new idea? “Saturn might hold the key,” Ohno says. Saturn is almost twice as far from the sun as Jupiter, and scientists calculate that the dust shadow that cooled Jupiter’s birthplace barely reached Saturn’s. If this is the case, it means that Saturn appeared in a warmer region and therefore should not have acquired ice of nitrogen, argon, krypton or xenon. On the other hand, if the two gas giants really formed in the cold beyond the current orbits of Neptune and Pluto, then Saturn should have a lot of these elements, like Jupiter.

Thanks to the Galileo probe, which plunged into the Jovian atmosphere in 1995, astronomers know these abundances for Jupiter. What is needed, the researchers say, is a Saturn-like mission. Unfortunately, in orbit around Saturn, the Cassini probe (ND: 08/23/17) only measured an uncertain level of nitrogen in the ring planet’s atmosphere and detected no argon, krypton, or xenon, so Saturn has yet to limit where the two gas giants appeared.


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