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Comets: Siding Spring (C/2013 A1)

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NASA will hold a one-day NASA Social for up to 50 of its social media followers on Oct. 13, 2014, at the agency’s Jet Propulsion Laboratory in Pasadena, Calif.
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read the article 'Orbiter Completes Maneuver to Prepare for Comet Flyby'
NASA's Mars Odyssey spacecraft has successfully adjusted the timing of its orbit around Mars as a defensive precaution for a comet's close flyby of Mars on Oct. 19, 2014.

Comet Siding Spring Encounter at Mars Timeline

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Several weeks prior to closest approach

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July 2

MRO orbit maneuver to put spacecraft behind Mars.

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August 5

Odyssey orbit maneuver to put spacecraft behind Mars.

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September 19

Comet Siding Spring Science Workshop:
latest observations and plans for Mars spacecraft.

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September 21

MAVEN Orbit Insertion.

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September 24

Mars Orbiter Mission (MOM) goes into orbit around Mars.

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September 25

MRO orbit maneuver to put spacecraft behind Mars.

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10 days to closest approach

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October 7

MRO CRISM and HIRISE imaging of comet, to check comet trajectory.

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October 9

MAVEN last course correction to put spacecraft behind Mars.

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5 days to closest approach

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October 16

MAVEN's first science observation; ultraviolet (UV) images of the comet (with the IUVS). Other MAVEN instruments may study the comet to map the comets' coma, study the solar wind interaction, and possibly detect dust.

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October 17-19

MRO (MARCI, MCS and SHARAD) studies Mars' atmosphere to identify its nominal state. All cameras are on (HiRISE, CRISM, CTX) and will take images of the comet to determine the nucleus rotation rate.

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October 17-19

MAVEN will also look at the planet for temperature changes and solar-wind/gas interactions within the Mars upper atmosphere.

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October 17-19

Curiosity will image comet at night using the ChemCam camera to study the mineral makeup of the comet (note: ChemCam can't face the sun and it's difficult to move the mast camera at night). Opportunity will image the comet with PanCam.

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1 hour prior to closest approach

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October 19

MAVEN goes into planned "minimum risk" mode 1 hour prior to closest approach; fields and particles instruments will be on (SEP, MAG, LPW); all instruments requiring high voltage will be off.

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October 19

MRO final imaging prior to closest approach; CRISM and HiRISE to image the nucleus and CTX rides-along. Other instruments (MCS, MARCI, SHARAD) take observations of Mars' atmosphere.

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October 19

Odyssey last orbit before closest approach and thermal imaging by the THEMIS instrument of the coma.

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During closest approach

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October 19

MRO to image comet nucleus with CRISM and HiRISE (images may only be a few pixels).
CTX rides-along.

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October 19 11:28 a.m.
PT/2:28 p.m. ET/18:28 UT

Comet Siding Spring (C/2013 A1) closest approach to Mars at ~82,000 miles (132,000 kilometers).

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October 19 – closest approach

Opportunity and Curiosity will image the comet during closest approach.

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After closest approach

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October 19 closest approach + 20 minutes

Mars will skirt the comet coma.

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October 19 closest approach + 90 minutes

Odyssey will take several thermal images of the comet and tail

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October 19 closest approach + 90 minutes

MRO (CRISM and HiRISE) to image the nucleus and CTX rides-along. Other instruments (MCS, MARCI, SHARAD) take observations of Mars' atmosphere to identify atmospheric interactions with comet particles.

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October 19 closest approach + 2 hours

MAVEN will leave "minimum risk" mode. Spacecraft and instrument status will be checked over the next orbit, then science observations of Mars will resume, to get "after the comet" observations.

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October 20

Opportunity and Curiosity may image the comet after closest approach.

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October 20

Spacecraft will begin to report back to Earth their health and safety status (this schedule is still uncertain on which spacecraft will call home first).

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October 21

Odyssey images the comet with planet limb (best possible pretty picture).

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October 22

MRO will take its last images of comet.

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October 22

MAVEN completes its post-comet check on spacecraft and instruments.

*Descriptions are current as of 9-18-14 but are subject to change.

Comet Siding Spring Facts



This comet sneaked up on us because it was coming in from underneath the plane of Earth's orbit!

Luckily, asteroid and comet hunter Robert H. McNaught spotted it with the constellation Lepus in the star background.

At the time of its discovery, Comet Siding Spring
was farther from the Sun than Jupiter -
about 7.2 times farther away from the Sun than Earth.

McNaught achieved this triumph on January 3, 2013, using the .05-meter (20-inch) Uppsala Schmidt Telescope, at Siding Spring Observatory in New South Wales, Australia.

Anatomy of Comet Siding Spring (C/2013 A1)

Dust Tail

Comet Siding Spring's dust tail will completely engulf the entire planet when Mars travels through it. Hubble images show Comet Siding Spring has passed the snow and water lines, the points at which the Sun's warmth activates or releases gases and water ice to form the coma and tail.

Gas and dust in the comet's nucleus and coma often separate into two parts of the comet's tail. A comet's dust tail is the trail of dust and gas illuminated by the Sun. It is blown away from the comet's coma by the solar wind, and follows the curve of the comet's orbit.

When comets are traveling through the outer solar system, they are frozen and do not have tails. Far away and extremely small, they are almost impossible to detect. As they approach the Sun in the inner solar system, radiation from the Sun turns some comet materials like water ice into a gas. As gases leave the nucleus, they carry comet dust with them.

When sunlight illuminates the coma and tail as the comet approaches the Sun, astronomers have a better chance of detecting it.


Though early estimates suggested the size of comet Siding Spring's nucleus could be anywhere from 0.62 to 31 miles (1 to 50 kilometers) across, new data from NASA's Swift Satellite indicates that the icy nucleus of comet Siding Spring is only about 2,300 feet (700 meters) across. Hubble images of Comet Siding Spring show two jets coming from the icy nucleus in opposite directions. Measuring them can help us understand how the comet is rotating and what it might look like when it flies by Mars.

The nucleus is the solid, frozen core of a comet. It is made of rock, dust, water ice, and frozen gases (e.g., carbon dioxide, carbon monoxide, methane, and ammonia).

The nucleus of a comet is usually small in size, usually about a few miles across.

The surface of a comet's nucleus is often dry, dusty, rocky, and dark. Dark materials may contain organic compounds, the chemical building blocks of life. When a comet absorbs heat from the Sun, the nucleus releases water ice and frozen gases.

Sometimes, dazzling jets of gas can erupt from inside the nucleus when the Sun heats some parts of its surface more than others. That can cause the nucleus to spin or even break up into smaller pieces. Such events can change a comet's trajectory and, ultimately, its fate.


Comet Siding Spring has crossed the snow and water lines, key points when it is close enough for the Sun's warmth to activate it. Now that scientists can see the coma, they estimate it is roughly 12,000 miles (19,000 kilometers) across.

A comet's coma is the atmosphere of gas and dust around the nucleus of the comet. It can be hundreds of thousands of kilometers wide.

The coma of a comet is made largely of water and dust. When a comet approaches the Sun, it warms up. Heat from the Sun changes the comet's icy materials to gases. The comet releases these gases, forming the coma.

Radiation from the Sun and the solar wind then push a lot of this material away from the nucleus, forming the comet's tail.

When a comet is about the same distance from the Sun as Mars (about 1.5 AU), its coma can shrink, even though it is producing more gas as it warms. That's because the solar wind becomes forceful enough to push more coma material into the tail, making the tail a lot bigger.

That can be a big deal for planets like Mars, which is crossing through the debris field of Comet Siding Spring's coma and tail.

Ion Tail

Scientists will study Comet Siding Spring's ion tail to assess any effect ion-tail particles might have on Mars and Mars missions.

Comets usually have two tails-a dust and an ion tail.

The ion tail is made of ionized gas. (You've heard of solid, liquid, and gas, but there's a fourth state: ionized gas, or plasma. Think of plasma screens, fluorescent and neon lights, and even the Northern Lights). Gas becomes ionized when electrons are charged enough to escape atoms or molecules. That always causes a glow of some kind.

Gas in a comet becomes ionized when ultraviolet radiation from the Sun interacts with the comet's gases. A comet's ion tail is usually blue in color due to the gas molecules that make it up. Ionized gas gets blown away from the coma by the solar wind. A comet's ion tail always points away from the Sun.



The Comet Siding Spring (C/2014 A1) Science Workshop September 19, 2014

View archived webcast Part 1 | Part 2 | Part 3

Session 1: Setting the Stage/Observations from Orbit
View Content >>
Welcome; Agenda Fast & Zurek NASA HQ, JPL Presentation (PDF)
Webcast (2:38) >>

Intro and Logistics

Chandra and Kepler observing plans
Lisse JHU/Applied Physics Lab Presentation (PDF)
Webcast (20:38) >>
Webcast (9:40) >>

Current observing plans Kelley University of Maryland Presentation (PDF)
Webcast (14:47) >>

HST observing program issues Li Planetary Science Institute Presentation (PDF)
Webcast (20:59) >>

Latest SWIFT results Bodewits U Maryland Presentation (PDF)
Webcast (13:31) >>

Session 2: Comet Trajectory and Effects (current and expected)/Mars Mission Status
View Content >>
Comet ephemeris update Farnocchia JPL Presentation (PDF)
Webcast (15:21) >>

Latest SSERVI results: Phobos/Deimos ejecta Horanyi U Colorado, Boulder Presentation (PDF)
Webcast (16:10) >>

Mars Mission status overview Zurek JPL Presentation (PDF)
Webcast (6:43) >>

Integrated timeline of Mars-project observations of the comet Diniega JPL Presentation (PDF)
Webcast (21:17) >>

Mars Orbiter Mission: observation plans Bhardwaj Indian Space Research Organisation (ISRO) Presentation (PDF)
Webcast (22:12) >>

Mars Express: observation plans Svedhem European Space Agency (ESA) Presentation (PDF)
Webcast (1:12) >>
Webcast (18:18) >>

Session 3: Mars Mission Status
View Content >>
Mars Odessy: THEMIS observations Plaut JPL Presentation (PDF)
Webcast (15:37) >>

MRO: HiRISE observations Delamere Delamere Space Sciences Presentation (PDF)
Webcast (24:17) >>

MRO: CRISM observations Humm JHU/Applied Physics Lab Presentation (PDF)
Webcast (16:48) >>

Ground-based amateur observations of the Mars-Comet Encounter Yanamandra-Fisher Space Science Institute Presentation (PDF)
Webcast (19:35) >>

Observations of CSS from SOAR Samarasinha  Planetary Science Institute Presentation (PDF)
Webcast (13:57) >>

Discussion and Wrap-up Lisse, Zurek, Fast JHU/APL, JPL, NASA HQ Webcast (21:23) >>

The Comet Siding Spring and Its Close Approach to Mars Observer's WorkshopAugust 11, 2014

Session 1: Setting the Stage; Spacecraft Observations
View archived webcast >>
Session 2: Suborbital & Spacecraft Observations
View archived webcast >>
Session 3: Earth-based Observations
View archived webcast >>
Session 4: Mars-based Observations
View archived webcast >>