Dr. Gisela N. Ortiz León, a Postdoctoral researcher from Max Plack Institute for Radio Astronomy, along with an internal team of astronomers, made a wonderful discovery by finding a Saturn-like planet, which is orbiting a small, cool star. They were able to detect a ‘wobble‘ in the star’s motion, probably caused due to the gravitational pull of the planet.
Also, this is the 1st time that astronomers were to obtain observations by using this technique, employees with radio wavelengths. To make this possible, researchers created a network of radio antennas, linked them together, and formed a continent-sized telescope. They took highly precise measurements of the star’s position, which was only possible because of the radio telescope network.
TVLM 513b Planet
What makes this discovery fascinating is that the TVLM 513 b planet has a similar mass to Saturn, but its orbit analogous matches with the Mercury in our Solar System. So far, very few extrasolar planets with characteristics like that of TVLM 513 b got discovered around small, cool stars. These stars are also known as ultracool dwarfs.
The success rate of the techniques used by scientists to study these dwarfs was low due to the object’s faintness. That’s why researchers decided to utilize the radio observation technique, which proved to be a powerful and complementary tool to discover more new planets. If you read the ‘Astronomical Journal,’ you can find all the results related to the planetary study.
The Astrometric technique
By using the supersharp radio observation technique, astronomers made a continent-wide Very Long Baseline Array (VLBA) telescope and discovered a Saturn-sized planet. It is closely orbiting an ultracool dwarf, which is 35 light-years away from Earth. It is also the first time that astronomers discovered an extrasolar planet with a radio telescope and using a technique that needs highly precise measurements of the position of a star in the sky. It’s also the second planet discovery for that technique and radio telescopes.
This technique has been known for a very long time, but very difficult to use. The scientists have to track star’s actual motion in space, then detect minuscule wobble that took place in the motion, because of the gravitational effect of a planet. The planet and star orbit a location, also known as the center of mass, for both combined.
It becomes easy to detect the planet when the barycenter is far from the star’s center, which causes wobble to get detected by a telescope. The astrometric technique is good for detecting Jupiter-like planets in orbits distant from the star.
Note: When a massive planet orbits a star, it produces a wobble in the star that increases with larger separation between the star and plant. The more massive the planet at a given distance from the star, the larger the wobble produced.
From June 2018 to almost a year and a half, astronomers were tracking TVLM 513-46546 star, which is a cool dwarf whose mass is less than the 1/10th the mass of our Sun. They also analyzed data dated between March 2010 and August 2011, taken from previous VLBA observations. After analyzing the data, astronomers found the telltale wobble in the star’s motion, which indicated the presence of a planet, orbiting the star every 221 days. The distance between the planet and the star is the same as that of Mercury and the Sun. Its mass is also equal to Saturn.
TVLM 513-46546 ultracool dwarf Star
The ultracool dwarfs like TVLM 513-46546 are plenty in our Milky Way Galaxy, and many of them also have smaller planets like Mars and Earth (based on mass and size). Bigger planets like Saturn and Jupiter are very rare to be around small stars like TVLM 513-46546. Also, the astrometric technique is a perfect way to discover Jupiter-like planets in wide orbits.
It was a surprise for astronomers to find a Saturn-like planet with a lower mass in a compact orbit. Salvador Curiel, a researcher of the National Autonomous University of Mexico, said: “It was a great challenge to detect the orbital motion of a sub-Jupiter mass planetary companion in a compact orbit.” Till now, 4300+ planets have been discovered that are orbiting stars other than the Sun, but the planet orbiting around TVLM 513-46546 is only the second that’s found using the astrometric technique.
Another method known as the radial velocity technique relies on the gravitational effect of the planet on the star. This technique is able to detect slight acceleration in the star’s motion, either toward or away from Earth. (The acceleration caused by star’s motion around the barycenter.)
The astrometric technique got its recognition in the early 19th century as a means to discover extrasolar planets. A number of such techniques were announced over the years, but they failed at some point and got discontinued. The astrometric method is one of the oldest techniques to survive this long because of the success rate.
Amy Mioduszewski, a researcher at National Radio Astronomy Observatory, said: “The VLBA along with antennas separated by as-much-as 5,000 miles, provided us with high precision and resolving power needed to discover this extrasolar planet. Also, improvements made in VLBA’s sensitivity gave us information quality that made it easy for us to work now.“