Strange Stellar Spirals Could Hide Baby Exoplanets

Artist's illustration of a protoplanetary disc and a young star. Can we spot giant planets from the patterns in spirals?

When planets are in the process of being born, they grow from clouds of gas and dust surrounding their young star. However, penetrating this dense region to see planets coming to be, or to understand if planets outside of the dust are influencing them, is a difficult task.

To face this challenge, new research has found that some spiral patterns in the dust could, however, be evidence of huge planets swimming in its midst.

Scientists observed a protoplanetary disc around star MWC 758, using the ground-based Very Large Telescope. They found a spiral pattern that could suggest a planet lurking nearby. It's about 1.7 times the mass of our sun and only 8 million years old, a youngster compared to the sun's 4.5 billion years. The planet is believed to be outside the arms at about five times Neptune's equivalent distance from the sun.

"Our model with a 10 Jupiter mass planet is the best (and I would say the only) model so far to be able to account for all the major aspects of the arms as seen in the observations," wrote lead author Ruobing Dong, a NASA Hubble Fellow at Lawrence Berkeley National Laboratory and the University of California, in an e-mail to Discovery News. "Also, in such a young system, it is quite reasonable to believe there are giant planets currently forming. 10 Jupiter mass planets have been found around other (much older) stars, for example HR 8799."

A protoplanetary disc around MWC 758, a young star, based on observations from the European Southern Observatory's Very Large Telescope. The spiral arms are each about 10 billion miles long, or more than three times the diameter of Neptune's orbit.

The challenge is these features are hard to spot. You need to be able to see extremely fine detail, which can only be achieved by the Hubble Space Telescope and a few 8-meter ground based telescopes, Dong said. Worse, the light from the star can wash out the details in the disc. Adaptive optics on Earth can help account for that, but such a system to reduce the star's glare does not exist on Hubble.

The James Webb Space Telescope, which launches in 2018, should "in principle" be able to block out the light of the star and perhaps be able to better see these features than Hubble. The challenge, however, is it observes at longer wavelengths of light than Hubble and ground-based telescope, which makes the resolution more blurry. "Without carrying out detailed simulations to examine the predicted performance of JWST in this sort of observations, I would just say it might (work), but not sure," he added.

But if we were to see better in these systems, it would complement all the Kepler space telescope observations of older stars that we already have in hand. We would understand more about the older stars' history by looking at the youngsters, Dong said, using the analogy of observing business mogul (and presidential candidate) Donald Trump today versus when he was a child.

This computer model attempts to duplicate the structure seen in MWC 758. The "X" marked in the picture is where a planet supposedly lurks, unseen among all the dust and creating the arms.

"You don’t know what kind of baby he was when he was two years old," Dong said. "Did he cry a lot? Was he friendly to his playmates in day care? What kind of fairy tales did he like? In one sentence, Kepler finds 70-year-old Trumps, while the significance of our research is that we want to find baby Trumps."

The shape of the arms tells us about the mass of the planet, which they estimate is about 10 times the size of Jupiter. A smaller planet would be too weak to make the arms the shape that we see, according to the simulations, while a larger planet should already have been spotted in the disc, dusty as it is. Dong allowed, however, that there is some uncertainty in the calculations and the planet could be a slightly different mass than predicted.

Read more at Discovery News