Jupiter, left, and Saturn, right, are seen above a steeple after sunset from Arlington, Va., Tuesday, Dec. 22, 2020. The two planets are now slowly separating from each other in the sky, after appearing a tenth of a degree apart during the "great conjunction" on December 21. Photo Credit: (NASA/Bill Ingalls)

Saturn, top, and Jupiter, bottom, are seen after sunset from Alexandria, Va., Thursday, Dec. 17, 2020. The two planets are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Joel Kowsky)

Jupiter, left, and Saturn, right, are seen after sunset from Alexandria, Va., Tuesday, Dec. 22, 2020. The two planets are now slowly separating from each other in the sky, after appearing a tenth of a degree apart during the "great conjunction" on December 21. Photo Credit: (NASA/Joel Kowsky)

Saturn, top, and Jupiter, bottom, are seen after sunset from Alexandria, Va., Thursday, Dec. 17, 2020. The two planets are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Joel Kowsky)

Jupiter, left, and Saturn, right, are seen after sunset from Washington, DC, Tuesday, Dec. 22, 2020. The two planets are now slowly separating from each other in the sky, after appearing a tenth of a degree apart during the "great conjunction" on December 21. Photo Credit: (NASA/Aubrey Gemignani)

The Moon, left, Saturn, upper right, and Jupiter, lower right, are seen after sunset from Alexandria, Va., Thursday, Dec. 17, 2020. The two planets are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Joel Kowsky)

The Moon, left, Saturn, upper right, and Jupiter, lower right, are seen after sunset from Washington, DC, Thurs. Dec. 17, 2020. The two planets are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Aubrey Gemignani)

Jupiter, left, and Saturn, right, are seen during the “great conjunction” where the two planets appear a tenth of a degree apart from one another, Monday, Dec. 21, 2020, near Chapel Hill, North Carolina. Photo Credit: (NASA/Bill Ingalls)

Jupiter, left, and Saturn, right, are seen after sunset above Jordan Lake during the “great conjunction” where the two planets appear a tenth of a degree apart from one another, Monday, Dec. 21, 2020, near Chapel Hill, North Carolina. Photo Credit: (NASA/Bill Ingalls)

The Moon, left, Saturn, upper right, and Jupiter, lower right, are seen after sunset with the Washington Monument, Thurs. Dec. 17, 2020, in Washington. The two planets are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Bill Ingalls)

Jupiter, left, and Saturn, right, are seen during the “great conjunction” where the two planets appear a tenth of a degree apart from one another, Monday, Dec. 21, 2020, from Washington, DC. Photo Credit: (NASA/Aubrey Gemignani)

Saturn, top, and Jupiter, below, are seen after sunset from Shenandoah National Park, Sunday, Dec. 13, 2020, in Luray, Virginia. The two planets are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Bill Ingalls)

S84-40162 (21 Aug. 1984) --- Astronaut Anna L. Fisher controls the Remote Manipulator System (RMS) arm from inside the "orbiter" as part of her training program in the Johnson Space Center's Shuttle Mock-up and Integration Laboratory. Dr. Fisher, one of three mission specialists for mission 51-A, is inside the cabin portion of a trainer called the Manipulatory Development Facility (MDF). She is able to operate the arm in conjunction with an air bearing floor and to log a great deal of rehearsal time for her flight, on which the retrieval of a low-orbiting communications satellite is planned. Photo credit: NASA

The International Space Station is seen in this third of a second exposure passing between Saturn, top, and Jupiter, bottom, as it flies over Alexandria, Virginia, Friday, Dec. 11, 2020. Onboard are: NASA astronauts Kate Rubins, Shannon Walker, Victor Glover, Mike Hopkins; Japan Aerospace Exploration Agency (JAXA) astronaut Soichi Noguchi; Russian cosmonauts Sergey Ryzhikov, and Sergey Kud-Sverchkov. Saturn and Jupiter are drawing closer to each other in the sky as they head towards a “great conjunction” on December 21, where the two giant planets will appear a tenth of a degree apart. Photo Credit: (NASA/Joel Kowsky)

The first detection of Pluto in X-rays has been made using NASA's Chandra X-ray Observatory in conjunction with observations from NASA's New Horizons spacecraft. As New Horizons approached Pluto in late 2014 and then flew by the planet during the summer of 2015, Chandra obtained data during four separate observations. During each observation, Chandra detected low-energy X-rays from the small planet. The main panel in this graphic is an optical image taken from New Horizons on its approach to Pluto, while the inset shows an image of Pluto in X-rays from Chandra. There is a significant difference in scale between the optical and X-ray images. New Horizons made a close flyby of Pluto but Chandra is located near the Earth, so the level of detail visible in the two images is very different. The Chandra image is 180,000 miles across at the distance of Pluto, but the planet is only 1,500 miles across. Pluto is detected in the X-ray image as a point source, showing the sharpest level of detail available for Chandra or any other X-ray observatory. This means that details over scales that are smaller than the X-ray source cannot be seen here. Detecting X-rays from Pluto is a somewhat surprising result given that Pluto - a cold, rocky world without a magnetic field - has no natural mechanism for emitting X-rays. However, scientists knew from previous observations of comets that the interaction between the gases surrounding such planetary bodies and the solar wind - the constant streams of charged particles from the sun that speed throughout the solar system -- can create X-rays. The researchers were particularly interested in learning more about the interaction between the gases in Pluto's atmosphere and the solar wind. The New Horizon spacecraft carries an instrument designed to measure that activity up-close -- Solar Wind Around Pluto (SWAP) -- and scientists examined that data and proposed that Pluto contains a very mild, close-in bowshock, where the solar wind first "meets" Pluto (similar to a shock wave that forms ahead of a supersonic aircraft) and a small wake or tail behind the planet. The immediate mystery is that Chandra's readings on the brightness of the X-rays are much higher than expected from the solar wind interacting with Pluto's atmosphere. The Chandra detection is also surprising since New Horizons discovered Pluto's atmosphere was much more stable than the rapidly escaping, "comet-like" atmosphere that many scientists expected before the spacecraft flew past in July 2015. In fact, New Horizons found that Pluto's interaction with the solar wind is much more like the interaction of the solar wind with Mars, than with a comet. While Pluto is releasing enough gas from its atmosphere to make the observed X-rays, there isn't enough solar wind flowing directly at Pluto at its great distance from the Sun to make them according to certain theoretical models. There are several suggested possibilities for the enhanced X-ray emission from Pluto. These include a much wider and longer tail of gases trailing Pluto than New Horizons detected using its SWAP instrument. Because Pluto is so small compared to the size of a Chandra point source, scientists may be unable to detect such a tail in X-rays. Other possibilities are that interplanetary magnetic fields are focusing more particles than expected from the solar wind into the region around Pluto, or the low density of the solar wind in the outer solar system at the distance of Pluto could allow for the formation of a doughnut, or torus, of neutral gas centered around Pluto's orbit. It will take deeper and higher resolution images of X-rays from Pluto's environment than we currently have from Chandra to distinguish between these possibilities. http://photojournal.jpl.nasa.gov/catalog/PIA21061