Scientists Measure How Deep "Deep Impact" Was, With X-rays
X-ray Detections of Comet Tempel 1 Taken With Swift's X-ray Detector (XRT)
X-ray detections obtained by Swift on 7 July increased dramatically throughout the day. Swift scientists are continuing to monitor the X-ray emissions from Comet Tempel 1.
7 July: Light curve of Swift's X-ray detections from Comet Tempel 1 showing count rate (blue - before impact, red = after impact) The dramatic increase begins about 3-1/2 days after impact (300,000 seconds).
7 July: Swift's X-ray detections from Comet Tempel 1 taken before impact
7 July: Swift's X-ray detections from Comet Tempel 1 taken after impact
Here come the X-rays, on cue. Scientists studying the Deep Impact collision using NASA's Swift satellite report that comet Tempel 1 is getting brighter and brighter in X-ray light with each passing day.
The X-rays provide a direct measurement of how much material was kicked up in the impact. This is because the X-rays are created by the newly liberated material lifted into the comet's thin atmosphere and illuminated by the high-energy solar wind from the Sun. The more material liberated, the more X-rays are produced.
Swift data of the water evaporation on comet Tempel 1 also may provide new insights into how solar wind can strip water from planets such as Mars.
"Prior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source," said Dr. Paul O'Brien of the Swift team at the University of Leicester. "How things change when you ram a comet with a copper probe traveling over 20,000 miles per hour. Most of the X-ray light we detect now is generated by debris created by the collision. We can get a solid measurement of the amount of material released."
"It takes several days after an impact for surface and sub-surface material to reach the comet's upper atmosphere, or coma," said Dr. Dick Willingale, also of the University of Leicester. "We expect the X-ray production to peak this weekend. Then we will be able to assess how much comet material was released from the impact."
Based on preliminary X-ray analysis, O'Brien estimates that several tens of thousands of tons of material were released, enough to bury Penn State's football field under 30 feet of comet dust. Observations and analysis are ongoing at the Swift Mission Operations Center at Penn State University as well as in Italy and the United Kingdom.
Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting visible light, ultraviolet light, X-rays, and gamma rays. Different wavelengths reveal different secrets about the comet.
The Swift team hopes to compare the satellite's ultraviolet data, collected hours after the collision, with the X-ray data. The ultraviolet light was created by material entering into the lower region of the comet's atmosphere; the X-rays come from the upper regions. Swift is a nearly ideal observatory for making these comet studies, as it combines both a rapidly responsive scheduling system with both X-ray and optical/UV instruments in the same satellite.
"For the first time, we can see how material liberated from a comet's surface migrates to the upper reaches of its atmosphere," said Prof. John Nousek, Director of Mission Operations at Penn State. "This will provide fascinating information about a comet's atmosphere and how it interacts with the solar wind. This is all virgin territory."
Nousek said Deep Impact's collision with comet Tempel 1 is like a controlled laboratory experiment of the type of slow evaporation process from solar wind that took place on Mars. The Earth has a magnetic field that shields us from solar wind, a particle wind composed mostly of protons and electrons moving at hige velocity. Mars lost its magnetic field billions of years ago, and the solar wind stripped the planet of water.
Comets, like Mars and Venus, have no magnetic fields. Comets become visible largely because ice is evaporated from their surface with each close passage around the Sun. Water is dissociated into its component atoms by the bright sunlight and swept away by the fast-moving and energetic solar wind. Scientists hope to learn about this evaporation process on Tempel 1 now occurring quickly -- over the course of a few weeks instead of a billion years -- as the result of a planned, human intervention.
Swift's "day job" is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe. Swift's extraordinary speed and agility enable scientists to follow Tempel 1 day by day to see the full effect from the Deep Impact collision.
For the latest news on Swift analysis of comet Tempel 1, refer to:
http://swift.gsfc.nasa.gov
and
http://swift.sonoma.edu/
The Deep Impact mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.
CONTACTS:
John Nousek: nousek@astro.psu.edu, 814-865-7747
Paul O'Brien: pto@star.le.ac.uk, +44 116 252 5203
Dick Willingale: rw@star.le.ac.uk +44 116 252 3356
Lynn Cominsky: lynnc@universe.sonoma.edu, 707-664-2655
Barbara K. Kennedy (PIO), science@psu.edu, 814-863-4682
NASA Swift Satellite Offers a Different View of the Great Comet Collision
4 July 2005—Scientists using the Swift satellite witnessed a tale of fire and ice today, as NASA's Deep Impact probe slammed into the frozen comet Tempel 1. The collision briefly lit the dim comet's surface and exposed, for the first time, a section of ancient and virgin material from the comet's interior.
Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting optical light, ultraviolet, X-rays and gamma rays. Different wavelengths reveal different secrets about the comet.
So far, after a set of eight observations each lasting about 50 minutes, Swift scientists have seen a quick and dramatic rise in ultraviolet light, evidence that the Deep Impact probe struck a hard surface, as opposed to a softer, snowy surface. A movie of the ultraviolet observations is available at this web site (left) and at the Swift Mission Operations Center.
More observations and analysis are expected in the coming days from teams at NASA and Penn State and in Italy and the United Kingdom.
"We have now observed this comet before, during, and after the collision," said Dr. Sally Hunsberger of the Swift Mission Operation Center at Penn State. "The comparison of observations at different times -- that is, what was seen, when and at what wavelength -- should prove to be quite interesting."
Most of the debris observed in ultraviolet light likely came from once-icy surface material heated to 2,000 degrees by the impact. X-rays have not been detected yet but analysis will continue throughout the week. X-rays are expected to be emitted from newly liberated sub-surface material lifted into the comet's coma, which is then illuminated by the high-energy solar wind from the Sun. It takes about a day, however, for the material to reach the coma.
"Some called it fireworks today, but it really was more like 'iceworks,'" said Prof. Keith Mason, Director of Mullard Space Science Laboratory at University College London, who organized the Swift observations. "Much of the comet is ice. It's the other stuff deep inside we're most interested in -- pristine material from the formation of the solar system locked safely below the comet's frozen
surface. We don't know exactly what we kicked up yet."
Swift's "day job" is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe, far more energetic "fireworks." Indeed, since beginning this Deep Impact campaign on July 1 -- in addition to seeing comet Tempel 1 -- Swift has seen a gamma-ray burst and a supernova and has discovered a black hole in the Milky Way galaxy. The satellite's speed and agility, however, provides an important complement to the dozens of other world-class observatories in space and on Earth observing the Deep Impact experiment. Swift will continue to monitor the comet this week.
Comets are small astronomical objects usually in highly elliptical orbits around the sun. They are made primarily of frozen water, methane and carbon dioxide with a small amount of minerals. They likely originate in the Oort Cloud in the outskirts of the solar system. Comet Tempel 1 is about the size of Washington, D.C. Some scientists say that comets crashing into Earth billions of years ago brought water to our planet.
A comet becomes visible when radiation from the Sun evaporates its outer layers, creating a coma, the thin atmosphere. Solar wind impacts the coma to form the comet's tail of dust and gas, which always points away from the Sun. Comets are best visible when they enter the inner solar system, closer to the Sun.
"The Deep Impact collision was the most watched astronomical event of the year," said Dr. Neil Gehrels, Swift Principal Investigator at NASA Goddard Space Flight Center in Greenbelt, Md. "All the 'big-guns' observatories tracked it. In the next few days, as material continues to fly off the comet from newly created vents, we will see whether Swift can offer new insight into comets by virtue of the high-energy light we are seeing."
Prof. Mason and Prof. Alan Wells of the University of Leicester in England are at the Swift Mission Operation Center to help with the observation.
The Deep Impact mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.
MORE INFORMATION:
http://swift.gsfc.nasa.gov
and
http://swift.sonoma.edu
CONTACTS:
Margaret Chester: chester@astro.psu.edu, 814-8685-7746
Sally Hunsberger, sdh@astro.psu.edu, 814-865-7748
Neil Gehrels: gehrels@milkyway.gsfc.nasa.gov, 301-286-6546
Lynn Cominsky: llynnc@universe.sonoma.edu, 707-664-2655
Barbara K. Kennedy (PIO), science@psu.edu, 814-863-4682
29 June (before impact): Movie showing the comet Tempel 1 tracking accross the sky on 29 June 2005 using the Swift Ultraviolet/Optical Telescope (UVOT) through an ultraviolet filter centered on 2600 Angstroms. This sequence covers 40 minutes of elapsed time.
4 July: This movie shows the sudden brightening and gradual decline in ultraviolet light during first four hours after the Deep Impact experiment on Comet Tempel 1.
4 July notes about the movie from the Swift team: "We scheduled a baseline observation to check the observing facilities and to make sure we could download the data from the spacecraft to the ground station (Malindi) and to the SDC (Swift Data Center) website. During this period (03:06 to 04:28 UT), we observed for 40 minutes using a UVW1 filter in event mode. We transferred the data, verified that the Comet was visible, and made sure that the count rate was not too high to damage the instruments on-board. The impact observation began at 05:21 for another 40 minutes in the same way that the baseline was performed. We collected a 2000 second image and splitted it into 20 images of 100 seconds each to create a sequence of images."
5 July: This chart shows the sudden brightening and gradual decline in ultraviolet light detected by Swift during the first 15 hours after the Deep Impact experiment on Comet Tempel 1. Gaps occur when Swift's 96-minute orbit takes it to the opposite side of the Earth from Comet Tempel.
1 July 2005: False-color image of Comet Tempel 1 taken on 1 July 2005 with the Swift Ultraviolet Optical Telescope. The picture was formed from images taken separately through V, B, U, and Ultraviolet filters and corrected for the comet's motion before being combined. As a result, the background stars appear as a series of images in different colours.
29 June 2005: Image of Comet Tempel 1 taken on 29 June 2005 using the Swift Ultraviolet/Optical Telescope (UVOT) through an ultraviolet filter centered on 2600 Angstroms. The image has been compensated for the motion of the comet on the sky, so its background stars appear as streaks on the sky instead of as points.