“This is the first unambiguous detection of a two-planet system carving a disk gap.”
That’s astronomer-speak for “We just photographed two baby planets feeding off of their mama star and we couldn’t be prouder!” Julien Girard of the Space Telescope Science Institute in Baltimore, Maryland, announced it this week in a paper he co-authored in the journal Nature Astronomy and in a press release. It’s the first-ever discovery of new planets growing by accumulating dust and debris from the disk that usually surrounds a young star. In this case, the star is PDS 70, a low-mass T Tauri (younger than 10 million years – in this case it’s 6 million years old) star in the constellation Centaurus about 370 light-years from Earth. Its disk has a large gap extending from about 1.9 to 3.8 billion miles and that’s where astronomers suspected there were baby planets growing.
“With facilities like ALMA, Hubble, or large ground-based optical telescopes with adaptive optics we see disks with rings and gaps all over. The open question has been, are there planets there? In this case, the answer is yes.”
The planets have the boring names PDS 70 b and PDS 70 c, Discovered last year, PDS 70 b is the innermost planet, orbiting at a distance of about 2 billion miles or about the same distance as Uranus is from our Sun. PDS 70 c was just discovered using the Multi Unit Spectroscopic Explorer (MUSE) spectrograph on the European Southern Observatory’s Very Large Telescope (VLT) and is about 3.3 billion miles from PDS 70. While in the same disk gap, PDS 70 b orbits the star twice as fast as PDS 70 c.
“We were very surprised when we found the second planet.”
As with so many discoveries, Sebastiaan Haffert of Leiden Observatory, lead author on the paper, says they were looking for something else when they found PDS 70 c. The technique being used was developed to study galaxies and star clusters at higher spatial resolution, but it turns out to be an excellent astronomers’ tool for peeking into the windows of star nurseries and watching baby planets. By looking for various wavelengths of light from hydrogen in the orbiting disk of debris, they can spot the early formation of gas giant planets.
In answer to the question that’s on everyone’s mind … the astronomers can’t determine the sex of the two new baby exoplanets. Of course, they don’t really care as long as they’re healthy.