Oddball Planet Found By Amateur Astronomer, Thanks to Albert Einstein

The Cosmic Companion
Nov 1 · 4 min read

Kojima-1Lb is a cool exoplanet, roughly 20 times more massive than the Earth. What’s remarkable is how this planet was discovered, and its connection to Albert Einstein.

Almost 1,650 light years from Earth lies Kojima-1L, a dwarf star roughly 60 percent as massive as the Sun. Around that star revolves a giant planet, slightly more massive than Neptune, or around 20 times more massive than our own world. The planet was discovered thanks, in part, to a natural phenomenon first predicted by famed physicist Albert Einstein.

In 1915, Einstein released the general theory of relativity, which stated (in part) that light bends around massive objects in space. This effect can result in gravitational lensing, in which light from distant bodies is bent by nearer bodies, as if the light were traveling through a lens. This process is known as gravitational lensing, and the phenomenon is frequently used to observe objects in the depths of space.

A drawing of part of our galaxy, showing a target star and a line of other worlds.
A drawing of part of our galaxy, showing a target star and a line of other worlds.
A diagram showing the relative position of Kojima-1L compared to other systems discovered through gravitational lensing. The inset photo is an artists impression of the system. Image credit: University of Tokyo

All Eyes Up!

On November 1, 2017, Japanese amateur astronomer Tadashi Kojima announced his accidental discovery of an unknown star seen in the constellation of Taurus, the Bull. Astronomers around the globe pointed their instruments to the body, quickly determining that the observations were the result of gravitational microlensing, a small-scale version of the gravitational lensing first predicted by Einstein.

Other astronomers determined that the newly-discovered star was passing in front of another star, located 1,000 light years “behind” Kojima-1L. By studying changes in brightness from the background star, researchers determined that a large planet (around 20 times more massive than than the Earth) is orbiting Kojima-1L.

“Microlensing is a technique that facilitates the discovery of distant objects by using background stars as flashlights. When a star crosses precisely in front of a bright star in the background, the gravity of the foreground star focuses the light of the background star, making it appear brighter. A planet orbiting the foreground object may cause an additional blip in the star’s brightness,” Jet Propulsion Laboratory explains.

A diagram explaining how light curves are read to detect exoplanets.
A diagram explaining how light curves are read to detect exoplanets.
A look at how gravitational microlensing can be used to detect exoplanets around other stars (image from story on a different exoplanet also discovered through microlensing). Image credit: NASA, ESA, and K. Sahu (STScI)

This world was found much closer to it’s parent star than most exoplanets discovered from gravitational lensing. The distance at which this world sits from its sun places it near the snow line, where liquid water is expected to turn to ice soon after the formation of planets.

Nearly every star in our galaxy is now thought to contain worlds from tiny planets like Mercury, to water worlds, potentially teeming with life. Planets like Kojima-1Lb are likely to be gas giants, similar to Jupiter and Saturn, researchers predict.

The accidental discovery of this body, under such exacting conditions, suggests other worlds, similar in size to Kojima-1Lb, could be common near the snow-line surrounding alien stars.


Bend Me, Shape Me…

This is not the first time that an exoplanet has been found using gravitational microlensing, but these events are short and conditions need to be exactly right for astronomers to view the events. Therefore, most planets found using this technique have been found lying in the direction of the galactic center, where most local stars can be seen. In this case, Kojima-1Lb sits in the opposite direction from the galactic core, toward the edge of the disc of our galaxy.

A simulation of gravitational microlensing from NASA Video.

Akihiko Fukui at the University of Tokyo led a study utilizing 13 telescopes across the globe to observe the star, including the 188-centimeter (75-inch) and 91 cm (36 inch) telescopes at the Okayama Astrophysical Observatory, on top of Mt. Chikurin-Ji, in the Okayama prefecture of Japan.

More than 4,000 planets are now confirmed in more than 3,000 solar systems. Nearly 4,700 potential worlds await confirmation. The newest planet hunter in space, the Transiting Exoplanet Survey Satellite (TESS), has already discovered 29 confirmed worlds, and cataloged more than 1,300 possible targets since its launch in April 2018.

“[F]ew doubt that there exist countless [other words]among the many billions of stars in our universe.That makes the coincidences of our planetary conditions — the single sun, the lucky combination of earth-sun distance and solar mass — far less remarkable, and far less compelling as evidence that the earth was carefully designed just to please us human beings.

Planets of all sorts exist.”
― Stephen Hawking, The Grand Design

This newly-discovered system is the closest exoplanet to the Earth ever found through microlensing, as well as the brightest (as seen from our home world). By studying the microlensing data, astronomers not only detected the presence of this world, but they were also able to determine the mass of the exoplanet.

The Kojima-1L system is an ideal target for future studies using current and next-generation telescopes and instruments, including the Subaru Telescope in Japan, or the Thirty Meter Telescope, currently under construction in Hawaii.

Analysis of the followup studies of Kojima-1Lb was published in The Astronomical Journal.


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Writing about space since I was 10, still not Carl Sagan. Mailing List/Podcast: https://thecosmiccompanion.substack.com

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