Cooking A Comet: NASA's Solar Observing Fleet To Watch Comet ISON's Journey Around The Sun

Such images will come both from STEREO and the joint European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO. Then, NASA’s Solar Dynamics Observatory, or SDO, will view the comet for a few hours during its closest approach to the sun, known as perihelion. The X-Ray Telescope on the JAXA/NASA Hinode mission will also be looking at Comet ISON for about 55 minutes during perihelion.

All of these observatories will have different views. STEREO-B will be the only one that sees the comet transit across the face of the sun. In SDO’s view, the comet will appear to travel above the sun, and the SDO instruments will point away from the center of the sun to get a better view for three hours on Nov. 28. In addition to learning more about the comet itself, these observations can make use of the comet as a tracer to show movement in the solar wind and solar atmosphere.

The dates of viewings by these observatories are as follows:

    Nov 21-28: STEREO-A Heliospheric Imager

    Nov 26-29: STEREO-B coronagraphs

    Nov 27-30: SOHO coronagraphs

    Nov 28-29: STEREO-A coronagraphs

    Nov 28: SDO

    Nov 28: Hinode

As the new comet C/2012 S1 (ISON) and the well-known short-period comet 2P/Encke both approach their closest distances to the Sun later this month, they are also passing close to the MESSENGER spacecraft now orbiting the innermost planet Mercury. Just this week, both comets have brightened sufficiently to be captured in images by MESSENGER’s wide-angle camera. This figure shows, on the left, images of Encke on three successive days from November 6 to November 8; on the right, images of ISON are shown for three successive days from November 9 to November 11. Both comets appear to brighten each day (top to bottom). The images were acquired by the Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) aboard NASA’s MESSENGER spacecraft.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Southwest Research Institute

Green circles indicate some of the brighter cataloged background stars in each image; yellow marks bracket the comets. The background stars are fixed in each image from top to bottom, so the motion of the comet relative to the stars is clear in each case. The images have been smoothed slightly to diminish the distracting sharp edges of the pixels.

MESSENGER is viewing these comets from a vantage point that is very different from that of observers on Earth. Comet Encke was approximately 0.5 AU from the Sun and 0.2 AU from MESSENGER when these images were taken; the same distances were approximately 0.75 AU and 0.5 AU, respectively, for ISON. More images will be obtained starting on November 16 when the comets should be both brighter and closer to Mercury.

The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft’s seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System’s innermost planet. During the first two years of orbital operations, MESSENGER acquired more than 150,000 images and extensive other data sets. MESSENGER is scheduled to continue orbital operations until late March 2015.

NASA’s Hubble Sees Comet ISON Intact

A new image of the sunward plunging comet ISON suggests that the comet is intact despite some predictions that the fragile icy nucleus might disintegrate as the sun warms it. The comet will pass closest to the sun on Nov. 28.

In this NASA Hubble Space Telescope image taken on Oct. 9, the comet’s solid nucleus is unresolved because it is so small. If the nucleus broke apart then Hubble would have likely seen evidence for multiple fragments.

Moreover, the coma or head surrounding the comet’s nucleus is symmetric and smooth. This would probably not be the case if clusters of smaller fragments were flying along. A polar jet of dust first seen in Hubble images taken in April is no longer visible and may have turned off.

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

This color composite image was assembled using two filters. The comet’s coma appears cyan, a greenish-blue color due to gas, while the tail is reddish due to dust streaming off the nucleus. The tail forms as dust particles are pushed away from the nucleus by the pressure of sunlight. The comet was inside Mars’ orbit and 177 million miles from Earth when photographed. Comet ISON is predicted to make its closest approach to Earth on Dec. 26, at a distance of 39.9 million miles.

Contacts and sources:

Karen C. Fox, NASA’s Goddard Space Flight Center