Where is 8P/Tuttle now (from: Heavens Above)?

2007 Dec 24 - We are preparing for the next mission (Jan 3, 2008):
the Quadrantid Multi-Instrument Aircraft Campaign

2007 Dec 23 - Global-MS-Net observer Jeff Brower of Vancouver, Canada, reported these radio forward meteor scatter counts (at 61.260 MHz), suggesting a peak around 20:30 UT.

2007 Dec 23 (0h UT) - The International Meteor Organization's live website reports a peak rate around ZHR = 25 /hr, albeit based on few visual observations. This rate is much higher than normal Ursid shower activity, confirming that an outburst did occur.

2007 Dec 22 (21:23 UT) - "So far captured 25 URS mean mag. +1.2 and 16 SPORADICS with mean mag. +1.4. The rates picked up a few hours ago, the latest 10 minute radio plot looks decend, may mean the peak was around 21:15 UTC, or is just a temporary drop." - Ilkka Yrjola, Finland.

Radio MS reflections recorded by Esko Lyytinen of Helsinki, Finland, on December 22. Time in UT. The period of outburst activity is marked.

2007 Dec 22 (21:01 UT) - " The weather here got cloudy this evening after I got the first (quite bright) Ursid into my video camera. I heard that Ilkka has it yet clear and has captured a number of Ursids. My radio data seems to been climbing clearly up. Let's see how will it behave." - Esko Lyytinen, Finland.

2007 Dec 22 (12:42:44 UT) - Brian Murahashi and Jim Albers captured this bright -5 magnitude 12:42:44 UT Ursid fireball (see below) from an observing site in the Santa Cruz Mountains, California.

Ron Dantowitz and Ari Atinizian at Fremont Peak Observatory.

2007 Dec 22 (12:42:44 UT) - Ron Dantowitz (Dexter and Southfield Schools), student Ari Atinizian (Dexter School), and Peter Jenniskens (SETI Institute) observed from Fremont Peak Observatory and captured the spectrum of a bright -4 magnitude Ursid meteor at 12:42:44 UT in the hours before the peak. The observing interval was from 06:00 to 14:20 UT, with dawn arriving before the onset of the outburst.

Peter Jenniskens points to two comets visible in the sky in small telescopes on the night of the Ursid shower maximum, December 22, 2007.

2007 Dec 20 - Spaceweather.com Ursid story.

2007 Dec 20 - The International Meteor Organization has set up a quick-look page to collect visual observations of the 2007 Ursid shower from ground-based observers worldwide.

2007 Dec 20 - Video podcast on how to observe the Ursid shower courtesy of NASA Ames.

2007 Dec 18 - The 2007 Ursid shower prediction paper offprint is now available (courtesy Chris Trayner, editor JIMO).

2007 Dec 16 - The Geminid shower peaked Dec. 12 - 15 and produced this peculiar video of a not-so-bright Geminid leaving a persistent train. This series of photos was taken with a Canon 400D (16mm f4 Zenitar) digital all sky camera, each 44 seconds exposed at ISO 1600, by Klaas Jobse / Dutch Meteor Society. More pictures at Spaceweather.com.

2007 Dec 14 - Comet Tuttle's rotation period has been determined.

2007 Dec 13 - Feature story on the Ursid meteor shower predictions.

2007 Dec 11 - The prediction paper has been accepted for publication in the Journal of the International Meteor Organization, and is now in press.

2007 Dec 10 - Results from the Aurigid Multi-Instrument Campaign were presented at the American Geophysical Union Fall Meeting in San Francisco today.

2007 Dec 10 - Ursid Meteors 2007 announcement IAU Telegram.

2007 Dec 02 - Latest shower outburst predictions point to 2 to 8.5 hour half-peak duration shower with peak rate of about ZHR = 40 - 70 Ursids/hr at 20.0 - 22.2 UT (most likely around 21.4 - 22.2 UT), Dec 22, if seen under ideal circumstances.

2007 Nov 30 - Ursid MAC mission has been given the green light.

2007 Nov 12 - Ursid comet to travel over M33 galaxy on night of Dec 30 17h UT - Dec 31 00 UT.

2007 Nov 03 - Ursid comet now magnitude +12.1, with 3.5 arcminute sized coma, in reach of 0.2-m reflectors according to data listed in International Comet Quarterly.

2007 April 22 - Ursid comet recovered at +20.3 magnitude by Carl W. Hergenrother using the 1.54-m telescope at Catalina Observatory, Arizona ( IAUC 8848).

URSID MAC mission statement: Measure the size distribution and spatial distribution of a cloud of debris that travels with the parent comet 8P/Tuttle to develop a prediction model for this uncharted stream of meteoroids, which is a satellite impact hazard, and to compare to the freshly ejected dust observed in astronomical observations of the comet.

Orbiting just outside of Earth is a big old, but seemingly whimpy, comet the size of comet 1P/Halley. This comet called 8P/Tuttle, some 15 km (10 miles) across, is suspected to be a captured Oort cloud comet and is now in a very stable 13.6-year orbit. It has been revolving the Sun now for many tens of thousands if not hundreds of thousands of years. The comet spews as much vapor as does comet Halley, but even in the very favorable upcoming return it makes just barely naked eye visibility because, unlike comet Halley, it does not create a big cloud of smoke. Instead of fine sand and dust, this comet ejects solid matter the size of pebbles and course sand grains that fall appart over time.

Some of this dust evolves into Earth's path and creates the Ursid meteor shower of December. By finding out the age of the shower, and the age of the comet, we can learn how the properties of comet dust change in the inner solar sytem due to collisions with the dust grains of the zodiacal cloud and space weathering effects from solar and cosmic radiation.

In December of 1945, a new meteor shower was discovered, active in the days around December 22nd, by meteor astronomers at Skalnate Pleso Observatory in what is now the Slovak Republic. The shower was initially known as the "Umids", some called it "Becvar's shower", but over time it came to be known as the "Ursids". The IAU has adopted the popular name "Ursids", even though the IAU's nomenclature rules would make these the "Ursae Minorids".

At the time, the shower was unusually active and it took until the year 2000, before it was discovered why: the Earth traveled through old dust trails of parent comet 8P/Tuttle ejected in the return of AD 1405 and 1392. This had happened in 1945 and again in 1986, and the predicted return in 2000 was confirmed by observations (see figure below). In all these years, the comet itself was far from the Earth, close to its furthest point along the comet orbit. Astronomers Peter Jenniskens and Esko Lyytinen [paper] showed that the trail of meteoroids took 600 years to evolve its node inwards from where the comet crossed the ecliptic plane (just outside of Earth's orbit) into Earth's path itself. During those 600 years, the dust stayed clumped, and moved in an orbit slightly longer than that of the comet, trapped in the 7:6 mean-motion resonance rather than the 15:13 resonance of the comet, so that after 600 years, the dust delayed the comet by half an orbit.

Counts of radio reflections during the Ursids in the years around the previous return of the comet to the Sun. 2007 is equivalent to the year 1993. Data: Ilkka Yrjola, Finland.

More unusual Ursid activity: Starting in 1993, Finnish amateur meteor astronomer Ilkka Yrjola of Kuusankoski, detected additional Ursid outbursts that were wider, with a Full-Width-at-Half-Maximum duration of about 8 hours (see figure). These outbursts coincided with the return of comet 8P/Tuttle to perihelion on 1994 June 25. The cause of these outbursts remains unknown.

Location of 8P/Tuttle dust ejected between AD 600 and AD 1500. Note how the model explains the aphelion outbursts, but does not account for outbursts at the time when the comet returns. Calculations by Esko Lyytinen and Markku Nissinen, Helsinki, Finland.

Will we see the outburst again this year? Models for ejection of dust in the past 1400 years don't think so (click on figure above for higher resolution version). On the other hand, these models can not explain the outbursts in 1993 and 1994. Indeed, the dust from those outbursts could be much older. The comet has been around for tens or hundreds of thousands of years and the dust could be very old.

Comparing the freshly ejected dust of 8P/Tuttle with that observed as Ursids many thousands of years later could provide valuable insight into what happens to comet dust over time, when it collides with the dust particles of the zodiacal cloud and is repeatedly heated by solar radiation.

There are no accurate models that predict the coming Ursid outbursts. Little is known about their cause. The predictions below (for December 22 in each year) are those given in Meteor Showers and their Parent Comets, a 790-page handbook on meteor showers by Peter Jenniskens and published by Cambridge University Press in 2006. That study calculated the peak time and peak rate of the Ursid outbursts based on how the planets juggle the younger dust trails around, as calculated by Esko Lyytinen. It is expected that the new observations will help to improve the predictions for future years.

 year   dE-dR Delta_a f_M Sol.Lon. (UT) ZHR
 2007  +0.082 -0.0175 1.0 270.48 20:00 29
 2008  +0.047 +0.2674 1.0 270.54 03:42 54
 2009  +0.096 +0.5435 1.0 270.38 06:00 23
 2010  +0.097 +0.8114 1.0 270.28 09:51 22

The applet also allows you to see the difference between staying downtown or moving out into the countryside to a dark and clear location. All rates were calculated by taking into account the Moon light, which is pretty bad during the Ursids.

Disclaimer: Make sure that Java is enabled. The duration, peak activity and time of the peaks are based on recent numerical models and past Ursid outburst observations, and may be in error by several hours in peak time, and an unknown amount in peak rate.

LINKS:

NASA Ames Research Center missions website

Aurigid MAC mission website

Further reading on Ursid shower (Chap. 16)