Tag: exomoons

A Young Planet Found That May Well Be Making Moons

An image made by the Very Large Telescope in Chile shows a forming planet, the bright spot at right. The overpowering light of the host star is blocked out by a coronagraph inside the telescope. (ESO/A. Müller et al.)

Astronomers have many theories about how planets are formed within the gas, dust, pebbles and gradually rocks of the circumstellar disks that encircle a star after it has been born.  While the general outlines of this remarkable process are pretty well established, many questions large and small remain unanswered.

One is how and when exomoons are formed around these planets, with the assumption that the process that forms planets must also give birth moons.  But the potential moons have been far too small for the current generation of space and ground telescopes to identify.

Now astronomers have detected something almost as significant:  a circumplanetary disk surrounding a young planet that appears to be in the process of making moons.  The moon itself has not been detected, but a forming planet has been found with a ring of dust and gas that surrounds it.  And within that circumplanetary disk, astronomers infer, a moon is possibly being formed.

“Our work presents a clear detection of a disk in which satellites could be forming,” said Dr. Myriam Benisty, an astronomer at the University of Grenoble and the University of Chile.

“The new … observations were obtained at such exquisite resolution that we could clearly identify that the disk is associated with {the exoplanet} and we are able to constrain its size for the first time,” she said in a release.

While the first detection of the planet was made via the European Southern Observatory’s Very Large Telescope in Chile, the more granular observation of the forming planet and its moon-forming disk was made with the Atacama Large Millimeter/submillimeter Array (ALMA), also in Chile.

This ALMA image shows the young PDS 70 planetary system. The system features a star at its center and at least two planets orbiting it, PDS 70b (not visible in the image) and PDS 70c, surrounded by a circumplanetary disk (the dot to the right of the star). Image credit: ALMA / ESO / NAOJ / NRAO / Benisty et al.)

The finding, published in the Astrophysical Journal Letters, came via direct imaging — in effect through extremely high power photography rather through the indirect methods much more common in exoplanet astronomy.… Read more

The Giant Moon That Might Be the Heart of a Jupiter

Artist’s impression of the exomoon candidate Kepler-1625b-i, the planet it is orbiting and the star. (NASA/ESA/L. Hustak, STScI)

“Moons are where planets were in the 1990s,” predicted René Heller from the Max Planck Institute for Solar System Research a few years ago. “We’re on the brink.”

Heller was predicting that we were close to the first discoveries of exomoons: moons that orbit extrasolar planets outside our solar system. When a possible exomoon detection was announced in 2017, Heller’s prediction was proved correct. Not only had we found a candidate moon, but its properties defied our formation theories just as with the discoveries of the first exoplanets.

However, a paper published in Science this month has proposed a method for building this most unusual of moons.

As we move away from the sun, the planets of our solar system become mobbed with moons. How these small worlds formed is attributed to three different processes:

Moons in our solar system are thought to have formed through three different mechanisms (E. Tasker / Many Worlds)

The most extensive moon real estate orbits our gas giants, Jupiter, Saturn, Uranus and Neptune. The majority of these moons are thought to have been born during the planets’ own formation, forming in disks of gas, dust and ice that circled the young worlds. These circumplanetary disks are like miniaturised versions of the protoplanetary disks that circle young stars and give rise to planets.

One exception to this is Neptune’s moon, Triton, which orbits in the opposite direction to the planet’s rotation. This retrograde path would not be expected to arise if Triton has formed out of a circumplanetary disk around Neptune, which always rotate the same direction as the forming planet. Instead, Triton was likely a dwarf planet that was snagged by Neptune’s gravity during a chance encounter.

The capture scenario has also been proposed for the two moons of Mars. The lumpy satellites resemble asteroids and may have been born in the asteroid belt that sits between Mars and Jupiter. However, both moons orbit the red planet in circular orbits that sit in the same plane, pointing to a more disk-like formation method. Although Mars is too small to have had a substantial circumplanetary disk during formation, a giant impact later in its history could have thrown debris into orbit. This debris disk could then have coalesced into the two moons.

Such a violent start to Mars’s moons would mimic the beginnings of our own moon.… Read more

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