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Pluto: X-ray Detection Sheds New Light on Pluto

  • Using Chandra, scientists have detected X-rays from Pluto for the first time.

  • During four observations between February 2014 and August 2015, low-energy X-rays from Pluto were found.

  • This X-ray emission comes from interaction between Pluto's atmosphere and a wind of particles from the Sun.

  • This result provides new insight into Pluto and its surrounding environment.

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 reported in our press release this result offers new insight into the environment surrounding the largest and best-known object in the solar system's outermost regions.

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 Horizons 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. 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.

A paper describing these results has been accepted and published online in the journal Icarus with Carey Lisse (Johns Hopkins University Applied Physics Laboratory) as its first author.

The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, designed, built, and operates the New Horizons spacecraft and manages the mission for NASA's Science Mission Directorate. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Fast Facts for Pluto:
Credit  X-ray: NASA/CXC/JHUAPL/R.McNutt et al; Optical: NASA/JHUAPL
Release Date  September 14, 2016
Scale  X-ray image is about 12 arcsec across (about 285,000 km).
Category  Solar System
Observation Date  24 Feb 2014; 26, 30 Jul & 01 Aug 2015
Observation Time  48 hours 20 minutes (2 days 20 min).
Obs. ID  15699, 17703, 17708, 17709
Instrument  ACIS
References Lisse, C.M. et al, 2016, Icarus (accepted)
Color Code  X-ray (Blue), Optical (Red, Green, Blue)
Distance Estimate  About 4.9 billion km (3 billion miles)
distance arrow
Visitor Comments (8)

What do you guys think it is?

Posted by Decota on Friday, 01.20.17 @ 11:02am

Dear Charles Szmanda,
A relatively narrow range of energies, 400-700 eV 18-30 Å which is how we determine that this is probably from specific atomic lines and not thermal continuous emission.

Posted by CXC on Friday, 10.7.16 @ 09:57am

Dear Brian,
Perhaps a few, they could cause fluorescence. But there are very few cosmic rays, relative to solar X-rays and Solar ions.

Posted by CXC on Friday, 10.7.16 @ 09:54am

Wouldn't comic rays hitting Pluto generate x-rays?

Posted by Brian on Monday, 10.3.16 @ 06:56am

Hi, I'm just curious about what the wavelength is for the x-rays coming off of Pluto. Is there a distribution or is that a single wavelength?

Posted by Charles Szmanda on Sunday, 09.18.16 @ 12:41pm

Thank you. My colleagues and I at Eastman Kodak's Image Acquisition Systems built Chandra's telescope. We called it AXAF.
So thank you for putting our work to such good use expanding our knowledge of our universe. We were proud of our work, your work makes us even prouder.
Steve A-G
Rochester, NY

Posted by Steve Alpert-Gillis on Sunday, 09.18.16 @ 08:05am

What a mistake demoting Pluto was. This article provides more evidence that Pluto is in fact a planet.

Posted by Michael Amato on Friday, 09.16.16 @ 22:28pm

Such beautiful pictures. Thank you.

Posted by JOHNNY REDWINE on Wednesday, 09.14.16 @ 18:22pm

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