If the solar system is a family, then some planets depart home as soon as possible. Whether they want to or not. Once they accept the gravity of their family, they decide to move the space between the stars forever, not unbound to any star.
Astronomers want to call these drifters “thug planets”, and they’re getting better at finding them. A team of astronomers has discovered one of these floating rogues that is about the same size as Mars or Earth.
Finding something in deep space that doesn’t have any light on it is extremely challenging. But the two organizations are doing the same. They are OGLE (ical optical gravitational lensing experiment) collaboration and KMTN (Korean Microlensing Telescope Network) collaboration.
Now, a team of scientists from both groups has announced the discovery of a low-mass rogue planet. There are no stars near it, and its distance from the earth is unconfirmed. The team says it is proving that microlensing technology is effective for detecting Earth-mass planets that are free-floating in space.
The paper, which presents the findings, is titled “Terrestrial-Mass Rogue Planet Candidate Found in Short-Term Microlensing Event.” 30 authors are listed as contributors to this work, and the main author is Prezak Schreiz, a postdoctoral scholar in astronomy at Caltech. This paper is available on the pre-press site arxiv.org.
Astronomers believe that in the early days of the solar system, some low-mass planets will be pulled out of the star’s gravitational pull. Things can get chaotic in the early days, and gravitational interactions between stars and all planets can send small planets out into space to defend themselves. The authors write, “According to planetary theories, such as core attraction theory, the typical mass of extraterrestrial planets should be between 0.3 and 1.0 Earth masses.”
Finding these tiny bodies in the vast darkness of space requires an innovative approach: gravitational lensing.
Gravitational lensing requires two things: a distant light source, usually an object object close enough to a mass to act like a star and lens, and to divert light from a light source. In this case, the low-mass planet acts as a lens. And depending on how much the light of a distant star is affected by the object in the foreground, astronomers can learn a little.
A relatively small object like a low-mass planet does not emit much light, and not for very long. In their paper, the authors state that “extremely small angular Einstein radii (.1 months) and very short-term (0.1 days) are expected in microlensing events due to terrestrial-mass rogue planets.” According to the authors, this is one of the most extremely short-lived microlenses ever discovered.
In the last few decades, the knowledge of exoplanets has exploded. We now know thousands of them, and we expect that almost every star orbits the planets. All of this knowledge has led to updated theories and models of the formation of planets and the solar system. And those models show that there must be a lot of rogue planets that were out of their systems.
Theoretical work shows that the Milky Way may have billions or even trillions of free-floating planets. In their work, the authors list the ways in which these planets can be orphaned: planet-planet scattering; Dynamic interactions between giant planets that lead to orbital disruption of smaller, inner planets; Interaction between stars in binary or trinity systems and star clusters; Stellar fly-bays; And the evolution of the host star is the main sequence.
Microlensing provides a way to detect these tiny rogue planets. But it is difficult. It’s not that they’re too slow or that’s the problem. This is because microlensing events for these small organizations are on a very short time scale due to their size. The newly discovered planet, dubbed “OGLE-2016-BLG-1928”, was found at a micro-lensing event that lasted only 41.5 minutes. It is not much time to collect detailed data.
Four other small rogue planets like this have been found before, in each short-term micro-lensing event. The authors write that these events together provide “strong evidence for the population of rogue planets in the galaxy.”
Researchers have had a hard time not only discovering this phenomenon, but also determining whether it was actually a planet.
“Unlike other short-term microlending events, we cannot deny the presence of a distant stellar companion,” he writes. They were able to exclude any stellar companion from a distance of only 8 AUS. But many planets orbit more than its stars.
The planet also “… discovered short-term microlensing events and found the current dish on the edge of the current limit,” the paper says. The authors say this indicates how difficult it is to detect these events. The event was also found with relatively few data points: only 15. (11 were of OGLE and 4 were of KMTN.)
The small number of data points in the search means that “the diminishing portion of the light curve is not covered by full observations.” The lack of that data means that there is some uncertainty around the nature of the microlensing event, and some uncertainty around having a planet really around it. Part of that uncertainty is from the background star itself.
The authors write, “The source star is located in the red-wide branch of the color intensity, and some spheres are known to produce stellar flares,” the authors write. Can they conclude on the flames of the stars as the cause of the event rather than a rogue planet?
“However, the properties of the event (its duration, amplitude and
Light curve shape) does not match the twinkling stars. “They conclude.
But despite the uncertainties, this discovery is still important. “Thus, the lens is one of the best candidates for the terrestrial-mass rogue planet found nowadays,” he writes. Although their mass measurements for their object are somewhat obscure, other properties of the phenomenon are “consistent with the existence of a lens sub-Earth-mass object without any stellar companion to the approximate distance of approximately one age from the planet.”
Disease planets have almost zero probability of planning life, so there will never be an intense field of study in the same way they would have become exoplanets. But they are still interesting, and like everything else, they have hints of how nature works.
In the future, the Nancy Grace Roman Space Telescope will assist in the discovery of rogue planets. There is a lot on his plate for his mission, including some huge themes like dark energy rays and some eagerly awaited actions like getting imaging exoplanets and spectra of their atmosphere.
But part of his job is to find floating rogue planets as small as Mars. The Ultra-Powerful Space Telescope will conduct a large microlensing survey to find more of these planets. Its findings will help us better understand how our own solar system holds for others.
“As our view of the universe has expanded, we have realized that our solar system may be unusual,” Samson Johnson, a graduate student at Ohio State University in Columbus, said in a press release. “Romans will help us learn more about how things fit into the cosmic scheme by studying the planets of the rogue.”
