Comet C/2013 A1 (Siding-Spring) is a dynamically new comet that will fly within 132,000 km of Mars. For the first time, spacecraft around Mars will get detailed images of the nucleus of a Dynamically New comet in the Fall of 2014. Part of a long-term campaign to study the behavior and evolution of Oort Cloud comets, Swift started observing the comet at a distance of 4.5 AU, and will follow it along its trajectory observing it every 0.5 AU until it leaves the inner solar system again.

Summary of Swift Results [Summarized in this presentation]:

Swift has observed Siding Spring at heliocentric distances of 4.5, 4, 3.5, 3.2, and 2.46 AU pre-perihelion. The first evidence of water was detected in observations acquired on May 27, 2014. Our results indicate a water production rates of 1.7E27 molecules/s, or ~50 kg/s [CBET 3888].  On July 10th, Swift measured a water production rate of 6.1e27 molecules/s, raising the minimum radius of the nucleus to 0.8 km. Swift continues to monitor the comet’s activity every month.


Comet C/2012 S1 (ISON) was a comet on its way to its first passage around the Sun. It was the first sun-grazing comet that could be followed from Saturn’s orbit to within a two million kilometer’s of the Sun. Predicted to be very bright, astronomers world wide kept keeping a close eye on the comet’s development. Part of our long-term campaign to study the behavior and evolution of Oort Cloud comets, Swift started observing the comet at a distance of 5 AU, and followed it along its trajectory.

    Swift was the first observatory to measure sensitive upper limits of the comet. From this we could estimate that ISON’s nucleus was relatively small - too small to survive its close encounter with the Sun, as it turned out.

Summary of Swift Results: (CBET 3608)

We obtained photometry using Swift/UVOT’s broadband V and UVW1 filters (2600 Å FWHM=700 Å) on Oct. 7, Oct. 20, Nov. 1, and Nov. 7 (rh = 1.52, 1.27, 0.98, and 0.83 AU). The observed OH coma corresponds to water production rates of 2.0e28, 1.8e28, 1.6e28, and 2.1e28 molecules/s ± 25%, respectively, based on a vectorial model. In fixed apertures of projected radius 50,000 km at the comet, we measured Afrho values of of 750, 796, 848, and 861 cm (+/- 5%), normalized to phase of 0 degrees using the phase function by D. Schleicher. In addition, we further processed the remote Swift-UVOT observations acquired in the first half of 2013 and lowered our upper limits for the comet’s water production rate. Using aperture radii between 10-20 arcsec, we find the following 3-sigma upper limits for Jan. 30, Mar. 11, Apr. 24, and May 9 (rh = 4.95, 4.50, 3.97, and 3.79 AU): QH2O <8e27, <2e27, <2e27, <1.e27 molecules/s.


TOP: Swift observations of Comet C/2012 S1 (ISON) while it was still far from the Sun. At a distance of 5 AU (750 million kilometers) from the Sun, the comet already had a clear tail - proving it was already active.

Credit: NASA/Swift/UMD/Bodewits

Comet C/2012 S1 (ISON)

Comet C/2013 A1 (Siding-Spring)

Dynamically new comet on its way to Mars

ABOVE: Still at 2.46 AU from the Sun, Swift detected evidence of water around comet Siding Spring. This provides an important clue to how active the comet will be at its closest approach to Mars.

Comet C/2014 E2 (Jacques) is a comet that likely passed through the inner solar system several times before. We will compare its behavior with new comets like ISON and Siding Spring to investigate how comets age.

Summary of Swift Results:

Swift has observed Jacques at 1.5 and 1 AU pre-perihelion. It will continue its spectroscopic and imaging observations at the end of July 2014 (1.0 - 1.5 AU).

Comet C/2012 K1 (Panstarrs)

How do comets evolve?

Comet C/2012 K1 (Panstarrs) is a bright comet which Swift started observing at 6 AU from the Sun. Dynamically new comets often behave different before and after they were first heated by the Sun. Panstarrs offers a unique opportunity to follow a new comet for a very long period. Trivia fact: C/2012 K1 passed the decommissioned Deep Impact spacecraft within 0.12 AU on Aug. 7, 2014.

Summary of Swift Results:

Swift already observed Panstarrs at 4.8, 4.0, 2.9, 2.4, and 1.9 AU pre-perihelion. It will continue its spectroscopic and imaging observations when the comet comes out of solar constraint (Sep. 2014).


Comet C/2014 E2 (Jacques)

Weathered Oort Cloud comet

LEFT: Swift observations of Comet C/2012 S1 (ISON) in November 2013, at 1 AU from the Sun. Swift used its filters to image the water (blue; OH) and dust (yellow) around the comet.

ABOVE: Swift observations of Comet SIDING SPRING showed that at 4.5 AU from the Sun, the comet had a gigantic tail of at least 2 million km long. We will keep close track of the comet’s activity as it zips by the Mars on Oct 2014.

Comet C/2013 US10 (Catalina)

Distant comet with great potential!

Comet Catalina is a Dynamically New comet that Swift can follow from 6 AU before perihelion until 6 AU after perihelion. This makes it a valuable target that allows us to compare its pre- and post perihelion behavior. The comet is expected to get very bright (mv ~ 4). Observations are scheduled for Aug. 12, 2014 (6 AU), Nov. 5 2014 (5 AU), and Jan. 1st 2015 (4.4 AU). 

Credit: NASA/Swift/UMD/Bodewits

Credit: NASA/Swift/UMD/Bodewits

ABOVE: Comet C/2014 E2 (Jacques) at 1.5 AU before perihelion.

Did not survive its trip from the Oort Cloud to the Sun

Credit: NASA/Swift/UMD/Bodewits