Hubble captures Comet ISON

The comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate.

By STScl, Baltimore, Maryland Published: April 24, 2013

Comet ISON is potentially the "comet of the century" because around the time the comet makes its closest approach to the Sun on November 28 it may briefly become brighter than the Full Moon. Right now the comet is far below naked-eye visibility, and so Hubble was used to snap the view of the approaching comet. // NASA/ESA/J.-Y. Li (Planetary Science Institute)/and the Hubble Comet ISON Imaging Science Team
This NASA Hubble Space Telescope image of Comet C/2012 S1 (ISON) was photographed April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles (621 million kilometers) from the Sun (394 million miles [634 million km] from Earth). Comet ISON could become the most remarkable comet in centuries when it travels into the inner solar system this fall.

Even at that great distance, Comet ISON is already active as sunlight warms the surface and causes frozen volatiles to sublimate. A detailed analysis of the dust coma surrounding the solid, icy nucleus reveals a strong jet blasting dust particles off the sunward-facing side of the comet’s nucleus.

Preliminary measurements from the Hubble images suggest that the nucleus of Comet ISON is no larger than 3–4 miles (5–6 kilometers) across. This is remarkably small considering the high level of activity observed in the comet so far, said researchers. Astronomers are using these images to measure the activity level of this comet and constrain the size of the nucleus in order to predict the comet’s activity when it skims 700,000 miles (1.1 million km) above the Sun’s roiling surface on November 28.

Comet ISON’s dusty coma, or head of the comet, is approximately 3,100 miles (5,000km) across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles (92,000km), far beyond Hubble’s field of view.

More careful analysis is currently underway to improve these measurements and to predict the possible outcome of the sungrazing perihelion passage of this comet.

This image was taken in visible light with Hubble’s Wide Field Camera 3. The blue false color was added to bring out details in the comet’s structure.

ISON stands for International Scientific Optical Network, a group of observatories in 10 countries who have organized to detect, monitor, and track objects in space.

This article originally appeared on and is reprinted here with permission from Kalmbach Publishing.