Astronomer develops new method for spotting elusive newborn planets

They are hard to spot underneath all the space dust.
Loukia Papadopoulos
New planets are being born all the time.jpg
New planets are being born all the time.


Astronomers today understand the basics of how planets are born but have struggled to witness the process thus far, even with the use of advanced tools.

Now, a group of astronomers at the Center for Astrophysics, Harvard & Smithsonian have engineered a new way to detect these elusive newborn planets, according to a press release by the institution published Thursday.

The findings are described in The Astrophysical Journal Letters.

Directly detecting newborn planets

"Directly detecting young planets is very challenging and has so far only been successful in one or two cases," said Feng Long, a postdoctoral fellow at the Center for Astrophysics who led the new study.

"The planets are always too faint for us to see because they're embedded in thick layers of gas and dust."

This means that scientists are left with no choice but to hunt for clues to infer a planet is developing beneath all the dust and rubble.

"In the past few years, we've seen many structures pop up on disks that we think are caused by a planet's presence, but it could be caused by something else too," Long said.

"We need new techniques to look at and support that a planet is there."

Long drew these conclusions after carefully studying a protoplanetary disk known as LkCa 15, located 518 light years away. There had been previous claims of the existence of planet formations in the disk that came about from observations with the ALMA Observatory.

Astronomer develops new method for spotting elusive newborn planets
Newborn planets are hard to spot.

Long examined high-resolution ALMA data on LkCa 15 from 2019 and spotted two faint but important features that had been missed by other astronomers looking at the data.

These were located at about 42 times the distance Earth is from the Sun and looked like a dusty ring with two separate and bright bunches of material orbiting within it.

A small clump and a larger arc

The best way to describe what she witnessed was that it was a small clump and a larger arc that were separated by 120 degrees. After further reviewing the vision with computer models, Long learned that the objects’ size and locations matched the model for the presence of a planet.

"This arc and clump are separated by about 120 degrees," she explained. "That degree of separation doesn't just happen -- it's important mathematically."

Unfortunately, the small, newborn planet cannot yet be directly imaged due to technological limitations, but Long hopes additional future ALMA observations of LkCa 15 will provide further evidence supporting her planetary discovery.

If so, this may mean that Long has stumbled on a revolutionary way to detect faraway newborn planets that could forever change how astronomers approach their search for celestial objects.

In the meantime, Long hopes her new method will be used by other astronomers to make more discoveries.

"I do hope this method can be widely adopted in the future," she said. "The only caveat is that this requires very deep data as the signal is weak."

Study abstract:

We present deep high-resolution (∼50 mas, 8 au) Atacama Large Millimeter/submillimeter Array (ALMA) 0.88 and 1.3 mm continuum observations of the LkCa 15 disk. The emission morphology shows an inner cavity and three dust rings at both wavelengths, but with slightly narrower rings at the longer wavelength. Along a faint ring at 42 au, we identify two excess emission features at ∼10σ significance at both wavelengths: one as an unresolved clump and the other as an extended arc, separated by roughly 120° in azimuth. The clump is unlikely to be a circumplanetary disk (CPD) as the emission peak shifts between the two wavelengths even after accounting for orbital motion. Instead, the morphology of the 42 au ring strongly resembles the characteristic horseshoe orbit produced in planet–disk interaction models, where the clump and the arc trace dust accumulation around Lagrangian points L4 and L5, respectively. The shape of the 42 au ring, dust trapping in the outer adjacent ring, and the coincidence of the horseshoe ring location with a gap in near-IR scattered light, are all consistent with the scenario of planet sculpting, with the planet likely having a mass between those of Neptune and Saturn. We do not detect pointlike emission associated with a CPD around the putative planet location (0farcs27 in projected separation from the central star at a position angle of ∼60°), with upper limits of 70 and 33 μJy at 0.88 and 1.3 mm, respectively, corresponding to dust mass upper limits of 0.02–0.03 M.