The Living Force
A bright fireball lit up the night sky over the Brazilian states of Sao Paulo, Parana, Santa Catarina and Rio Grande do Sul.
Published on May 26, 2022 (2:37)
Published on May 26, 2022 (2:37)
Electronic Telegram No. 5125
Central Bureau for Astronomical Telegrams
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TAU HERCULID METEOR SHOWER 2022 P. Jenniskens, SETI Institute and NASA Ames Research Center; Q. Ye, University of Maryland and Boston University; and J. Vaubaillon, I.M.C.C.E, Observatory of Paris, report that a meteor outburst of tau Herculid meteors (IAU shower 61) is anticipated for May 31 around 4h-5h UT this year. This outburst is unusual in that the debris was generated during the 1995 breakup of comet 73P/Schwassmann-Wachmann (cf., Luethen et al. 2001, J. Intl. Meteor Organization 29, 15-28). Independent calculations at I.M.C.C.E. and the University of Maryland, using slightly different inputs, now put the 1995 dust trail in the earth's path with an expected peak on May 31d05h01m and 03h52m UT, respectively. In both models, meteors will radiate from R.A. = 209 deg, Decl. = +28 degrees with an apparent velocity of 16.4 km/s (geocentric velocity 12.1 km/s). The outburst is expected to last about two hours. Observers in the continental USA and Mexico are most favorably located to see this event in new-moon conditions, with a radiant high in the northwest.
The authors note that there are two caveats. First, an unusual meteor shower will only happen if the meteoroid ejection velocities during the breakup and decay of fragments were a factor of 2.5 higher than under normal cometary ejection conditions. Because the comet itself is not near the earth, normal ejection does not have the meteoroids disperse far enough ahead of the comet to intersect the earth's path. The higher gas-production rate of comet 73P in 1995 suggests that ejection velocities may have been higher by up to a factor of 2.7. However, the ejection velocities of cm- and mm-sized meteoroids were not measured in 1995. Second, if the outburst happens, the meteors will be mostly faint. Rare tau Herculids are also known from regular cometary activity during normal returns. The Cameras for Allsky Meteor Surveillance (CAMS) project, which triangulates video-detected meteors visible to the naked eye, measured the orbit of 18 tau Herculids during dust-trail crossings in 2011, 2017/ and 2019; from this, the authors calculate a steep magnitude-distribution index of 5.4 +/- 1.1, meaning that there were five times more meteors of magnitude +4 than +3, five times more meteors of mag +3 than +2, etc. -- but with the camera sensitivity such that more meteors of magnitude +3 were detected. In practice, a few meteors were of magnitude +1, but most were near the +4 magnitude detection limit of the video cameras.
Calculations at the University of Maryland show that when the earth crosses the meteoroid stream, a very faint glow from scattered sunlight may be visible in the sky centered around R.A. = 170 deg, Decl. = +20 deg in Leo, and around R.A. = 355 deg, Decl. = -15 deg in the opposite direction in Equ. Finally, two dust trails from the normal 1892 and 1897 returns of 73P will also be in the earth's path around 16h UT on May 30 and 10h UT on May 31, respectively (cf., Wiegert et al. 2005, MNRAS 361, 638). Because the comet has been known only since 1930, these trail crossings could shed new light onto the past activity of the comet, if detected.
THE TAU HERCULID METEOR SHOWER ACTUALLY HAPPENED: Forecasters were right. Debris from Comet 73P/Schwassmann-Wachmann-3 did hit Earth last night. Observers across North America witnessed the resulting display of tau Herculid meteors. It was not a meteor storm, as some had hoped, but instead a gentle shower punctuated by bright flurries.
The Canadian Meteor Orbit Radar (CMOR) in western Ontario detected more than 30 slow tau Herculids. Take a look at their radar sky map; all of the meteors were clustered near Arcturus, as expected. Independent radio data reported by Japanese astronomers reveal two peaks of tau Herculid activity, perhaps linked to two distinct debris streams from Comet 73P/Schwassmann-Wachmann 3. It is noteworthy that these radio and radar detections include very small meteoroids too faint to see with the unaided eye.
One of the strongest meteor showers of the year is underway. You might not notice, though, because of the glare. The Canadian Meteor Orbit Radar (CMOR) is picking up significant activity less than 20 degrees from the sun.
Its source is sungrazing Comet 96P/Machholz, which has laid down a trail of debris in the early-June portion of Earth's orbit. When the shower peaks on June 7th, CMOR will detect approximately one Arietid every 20 seconds--a rate which ranks the Arietids among the top meteor showers of the year.
It turns out that June is the best month of the year for daytime meteor showers. When the Arietids subside, another daytime shower will take over: The zeta Perseids (ZPE) peak on June 13th. And then another: The beta Taurids on June 29th. If only we could see them...
The massive outburst of the comet 17P/Holmes in 2007 October is the largest known outburst by a comet thus far. We present a new comprehensive model describing the evolution of the dust trail produced in this phenomenon. The model comprises of multiparticle Monte Carlo simulation including the solar radiation pressure effects, gravitational disturbance caused by Venus, Earth and Moon, Mars, Jupiter and Saturn, and gravitational interaction of the dust particles with the parent comet itself. Good accuracy of computations is achieved by its implementation in Orekit, which executes Dormad-Prince numerical integration methods with higher precision. We demonstrate performance of the model by simulating particle populations with sizes from 0.001 to 1 mm with corresponding spherically symmetric ejection speed distribution, and towards the Sun outburst modelling.
The model is supplemented with and validated against the observations of the dust trail in common nodes for 0.5 and 1 revolutions. In all cases, the predicted trail position showed a good match to the observations. Additionally, the hourglass pattern of the trail was observed for the first time within this work. By using variations of the outburst model in our simulations, we determine that the assumption of the spherical symmetry of the ejected particles leads to the scenario compatible with the observed hourglass pattern. Using these data, we make predictions for the two-revolution dust trail behaviour near the outburst point that should be detectable by using ground-based telescopes in 2022.
You can download this paper for free: Evolution of the dust trail of comet 17P/Holmes (14 pages).
NASA's next-generation space observatory has sustained its first noticeable micrometeoroid impact less than six months after launch, but the agency isn't too concerned. The James Webb Space Telescope, also known as Webb or JWST, launched on Dec....www.sott.net
Wed, 08 Jun 2022 22:00 UTC
© Northrop Grumman
An artist's depiction of the James Webb Space Telescope at work.
NASA's next-generation space observatory has sustained its first noticeable micrometeoroid impact less than six months after launch, but the agency isn't too concerned.
The James Webb Space Telescope, also known as Webb or JWST, launched on Dec. 25, 2021. It has spent the intervening months trekking out to its deep-space post and preparing for science observations, a complicated process that has gone remarkably smoothly; recently, NASA said it expects to unveil the first science-quality images from the telescope on July 12.
Now, the agency announced on Wednesday (June 8) that the observatory has experienced its first few impacts from tiny pieces of space debris called micrometeoroids. But don't panic: Neither the observatory's schedule nor its scientific legacy is expected to suffer.
"With Webb's mirrors exposed to space, we expected that occasional micrometeoroid impacts would gracefully degrade telescope performance over time," Lee Feinberg, Webb optical telescope element manager at NASA's Goddard Space Flight Center in Maryland, said in the statement. "Since launch, we have had four smaller measurable micrometeoroid strikes that were consistent with expectations, and this one more recently that is larger than our degradation predictions assumed."
The most serious of the impacts occurred between May 23 and May 25 and affected the C3 segment of the 18-piece gold-plated hexagonal primary mirror, according to the statement.
All spacecraft are expected to experience and designed to withstand micrometeoroid impacts, and JWST is no different. The observatory's engineers even subjected mirror samples to real impacts to understand how such events might affect the mission's science.
However, the recent impact was larger than those that mission personnel had modeled or could test on the ground, according to the statement.
Despite the impact coming so early in the observatory's tenure, NASA officials are confident that the $10 billion telescope will still perform adequately.
Comment: They're 'confident' despite the impact being much larger and coming earlier than they'd expected: Russian space surveillance station records space activity surge in 2021
"We always knew that Webb would have to weather the space environment, which includes harsh ultraviolet light and charged particles from the sun, cosmic rays from exotic sources in the galaxy, and occasional strikes by micrometeoroids within our solar system," Paul Geithner, technical deputy project manager at NASA Goddard, said in the statement. "We designed and built Webb with performance margin — optical, thermal, electrical, mechanical — to ensure it can perform its ambitious science mission even after many years in space."
In addition, JWST launched with its optics in even better shape than the agency bargained for, officials noted in the statement.
Some micrometeoroid impacts can be predicted, officials wrote. For example, when the spacecraft is set to fly through known meteor showers, personnel can maneuver JWST's optical systems into safety for these events. However, the recent impact was not part of such a meteor shower and the statement classified it as "an unavoidable chance event."
After an impact occurs, engineers can individually adjust the 18 primary mirror segments on the observatory to keep the mirror as a whole finely tuned.
As the JWST team continues to evaluate the impact, NASA is focused on better understanding both the particular event and the environment that the observatory will experience throughout its mission. The telescope is orbiting what scientists call the Earth-sun Lagrange point 2, located nearly 1 million miles (1.5 million kilometers) away from Earth in the direction opposite the sun.
"We will use this flight data to update our analysis of performance over time and also develop operational approaches to assure we maximize the imaging performance of Webb to the best extent possible for many years to come," Feinberg said.