High resolution illustration of the Roman spaceship against a starry sky background. Credit: NASA’s Goddard Space Flight Center
New simulations show that NASANancy Grace’s Roman Space Telescope will be able to reveal numerous evil planets – free-floating bodies that are being orbited by our galaxy to a star. Studying these island worlds will help us understand more about how planetary systems form, evolve, and disintegrate.
Astronomers discovered planets outside our solar system, known as exoplanets, in the 1990s. We quickly went from knowing only our own planetary system to realizing that planets are probably the hundreds of billions of stars in our galaxy more or less. Now a team of scientists is finding ways to improve our understanding of planetary demographics by searching for rugged worlds.
“As our view of the universe expands, we realize that our solar system can be unusual,” said Samson Johnson, a student at State University in Columbus who is leading the research effort. “Novel will help us learn more about how we fit into the cosmic scheme of things by studying evil planets.”
The findings, published in the Astronomical Journal, centered on the ability of the Roman Space Telescope to locate and characterize isolated planets. Astronomers have so far only tentatively discovered a few of these nomadic worlds because they are so difficult to detect.
NASA’s Wide Field Infrared Survey Telescope (WFIRST) is now called the Nancy Grace Roman Space Telescope, after NASA’s first Chief of Astronomy. Credit: NASA
Find galactic nomads
Novel will find rough planets by conducting a large microlensing study. Gravitational lensing is an observational effect that occurs because the presence of mass warps the substance of space-time. The effect is extreme around very massive objects, such as black holes and entire galaxies. Even solitary planets cause a detectable degree of warping, called microlensing.
This animation shows how gravity microlensing can reveal island worlds. As an unseen rough planet passes for a distant star from our vantage point, the star’s light bends as it orbits the planet through the warped space-time. The planet acts as a cosmic magnifying glass, enhancing the brightness of the background star. Credit: NASA’s Goddard Space Flight Center / CI Lab
If a rough planet is closely related to a distant star from our vantage point, the star’s light will bend as it travels through the curved space-time around the planet. The result is that the planet acts as a natural magnifying glass, amplifying light from the background star. Astronomers see the effect as a spike in the brightness of the star as the star and planet agree. By measuring how the spike changes over time, shows clues about the mass of the rough planet.
“The microlensing signal of a rough planet lasts only between a few hours and a few days and is then gone forever,” said co-author Matthew Penny, an assistant professor of physics and astronomy at Louisiana State University in Baton Rouge. ‘This makes them difficult to observe from Earth, even with multiple telescopes. Novel is a game-changer for sugar planet seekers. ”
Microlensing offers the best way to systematically search for vulnerable planets – especially those with low masses. They do not shine like stars and are often very cool objects, emitting too little heat for infrared telescopes to see. These vagabond worlds are essentially invisible, but Roman will discover them indirectly through their gravitational effects in the light of distant stars.
Lessons from cosmic castles
Johnson and co-authors showed that Roman can detect hidden planets with large masses so small March. Studying these planets will help to narrow down competing models of planetary formation.
The planet building process can be chaotic, as smaller objects collide with each other and sometimes collide to form larger bodies. It is like using a piece of playdough to pick up other pieces. But every now and then, collisions and close encounters can be so violent that they fly a planet out of the gravity of its parent star. Unless it manages to drag on for a month, the newly created world is doomed to roam the galaxy alone.
This illustration shows a rough planet drifting through the galaxy alone. Credit: NASA /JPL-Caltech / R. Hurt (Caltech-IPAC)
Rogue planets can also form in isolation from clouds of gas and dust, similar to how stars grow. A small cloud of gas and dust could collapse to form a central planet instead of a star, with moons instead of planets around it.
Novel will test planetary formation and evolution models that predict different numbers of these isolated worlds. Determining the abundance and masses of vicious planets will provide insight into the physics that drives their formation. The research team found that the mission will deliver a rough planet count that is at least 10 times more accurate than current estimates, which range from tens of billions to trillions in our galaxy. These estimates come mainly from observations by ground-based telescopes.
Since Roman will observe above the atmosphere, nearly a million miles away from Earth in the direction of the Sun, it will provide far superior microlensing results. In addition to delivering a sharper view, Roman’s perspective will allow it to stare at the same patch of air for months at a time. Johnson and his colleagues showed that the microlending study of Roman will detect hundreds of vicious planets, although it will only search for a relatively narrow strip of the galaxy.
Part of the study involved determining how to analyze the mission’s future data to get a more accurate census. Scientists will be able to extrapolate from Roman’s cosmic planet count to estimate how often these objects are in the entire galaxy.
“The universe could shake with rough planets and we would not even know it,” said Scott Gaudi, a professor of astronomy at Ohio State University and a co-author of the paper. “We would never discover it without doing an in-depth, space-based microlysis study, as Roman will do.”
For more on this research, read Rogue Planets Could Outnumber the Stars.
Reference: “Predictions from the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey. II. Free floating rates for planetary detection ”by Samson A. Johnson, Matthew Penny, B. Scott Gaudi, Eamonn Kerins, Nicholas J. Rattenbury, Annie C. Robin, Sebastiano Calchi Novati and Calen B. Henderson, 21 August 2020, Astronomical Journal.
DOI: 10.3847 / 1538-3881 / aba75b
The Nancy Grace Roman Space Telescope is managed by Goddard, with the participation of NASA’s Jet Propulsion Laboratory and Caltech / IPAC in Pasadena, the Space Telescope Science Institute in Baltimore, and a team of scientists from research institutes in the United States.
