4,000th comet discovered by ESA and NASA Solar Observatory

Date:
June 17, 2020
Source:
NASA/Goddard Space Flight Center
Summary:
On June 15, 2020, a citizen scientist spotted a never-before-seen
comet in data from the Solar and Heliospheric Observatory, or SOHO
-- the 4,000th comet discovery in the spacecraft's 25-year history.



FULL STORY ==========================================================================
On June 15, 2020, a citizen scientist spotted a never-before-seen
comet in data from the Solar and Heliospheric Observatory, or SOHO --
the 4,000th comet discovery in the spacecraft's 25-year history.


==========================================================================
The comet is nicknamed SOHO-4000, pending its official designation
from the Minor Planet Center. Like most other SOHO-discovered comets,
SOHO-4000 is part of the Kreutz family of sungrazers. The Kreutz family
of comets all follow the same general trajectory, one that carries
them skimming through the outer atmosphere of the Sun. SOHO-4000 is on
the small side, with a diameter in the range of 15-30 feet, and it was extremely faint and close to the Sun when discovered -- meaning SOHO is
the only observatory that has spotted the comet, as it's impossible to
see from Earth with or without a telescope.

"I feel very fortunate to have found SOHO's 4,000th comet. Although
I knew that SOHO was nearing its 4,000th comet discovery, I did not
initially think that this sungrazer would be it," said Trygve Prestgard,
who first spotted the comet in SOHO's data. "It was only after discussing
with other SOHO comet hunters, and counting through the most recent
sungrazer discoveries, that the idea sunk in. I am honored to be part
of such an amazing collaborative effort." SOHO is a joint mission of
the European Space Agency (ESA) and NASA. Launched in 1995, SOHO studies
the Sun from its interior to its outer atmosphere, with an uninterrupted
view from its vantage point between the Sun and Earth, about a million
miles from our planet. But over the past two and half decades, SOHO has
also become the greatest comet finder in human history.

SOHO's comet-hunting prowess comes from a combination of its long
lifespan, its sensitive instruments focused on the solar corona,
and the tireless work of citizen scientists who scour SOHO's data for previously-undiscovered comets, which are clumps of frozen gases, rock
and dust that orbit the Sun.

"Not only has SOHO rewritten the history books in terms of solar physics,
but, unexpectedly, it's rewritten the books in terms of comets as well,"
said Karl Battams, a space scientist at the U.S. Naval Research Lab in Washington, D.C., who works on SOHO and manages its comet-finding program.



==========================================================================
The vast majority of comets found in SOHO's data are from its coronagraph instrument, called LASCO, short for Large Angle and Spectrometric
Coronagraph.

Like other coronagraphs, LASCO uses a solid object -- in this case, a
metal disk -- to block out the Sun's bright face, allowing its cameras to
focus on the relatively faint outer atmosphere, the corona. The corona
is critical to understanding how the Sun's changes propagate out into
the solar system, making LASCO a key part of SOHO's scientific quest to understand the Sun and its influence.

But focusing on this faint region also means LASCO can do something other telescopes can't -- it can see comets flying extremely close to the Sun,
called sungrazers, which are otherwise blotted out by the Sun's intense
light and impossible to see. This is why nearly all of SOHO's 4,000
comet discoveries have come from LASCO's data.

Like most who have discovered comets in SOHO's data, Prestgard is
a citizen scientist, searching for comets in his free time with the
Sungrazer Project.

The Sungrazer Project is a NASA-funded citizen science project, managed
by Battams, which grew out of comet discoveries by citizen scientists
early into SOHO's mission.

"I have been actively involved in the Sungrazer Project for about
eight years.

My work with sungrazers is what solidified my long-term interest in
planetary science," said Prestgard, who recently completed a master's
degree in geophysics from Universite' Grenoble Alpes in France. "I enjoy
the feeling of discovering something previously unknown, whether this is a
nice "real time" comet or a "long-gone" overlooked one in the archives."
In total, Prestgard has discovered around 120 previously-unknown comets
using data from SOHO and NASA's STEREO mission.



========================================================================== Copious comets This 4,000th comet discovery came earlier than scientists initially expected - - a byproduct of SOHO's teamwork with the Parker
Solar Probe mission. In coordination with Parker Solar Probe's fifth
flyby of the Sun, the SOHO team ran a special observation campaign in
early June, increasing the frequency with which the LASCO instrument
takes images of the Sun's corona, as well as doubling the exposure time
for each image. These changes in LASCO's imaging were designed to help
the instrument pick up faint structures that would later pass over Parker
Solar Probe.

"Since Parker Solar Probe was crossing the plane of the sky as seen from
Earth, the structures that we see from SOHO's coronagraphs will be in the
path of Parker Solar Probe," said Angelos Vourlidas, an astrophysicist
at the Johns Hopkins University Applied Physics Lab, in Laurel, Maryland,
who works on the Parker Solar Probe and SOHO missions. "It's the optimal configuration to do this type of imaging." These more-sensitive images
also revealed a number of comets that, based on their brightness,
would have been too faint to see in SOHO's regular, shorter- exposure
images. SOHO typically sees an uptick in comet discoveries each June,
because Earth's position in space places SOHO at a good angle to see
sunlight reflecting off of comets following the Kreutz path, a family of
comets that accounts for about 85% of the comets discovered by SOHO. But
this June saw 17 comets discovered in the first nine days of the month,
around double the normal rate of discoveries.

"Our exposure time is twice as long, so we're gathering way more light,
and seeing comets that are otherwise too faint for us to see -- it's just
like any long-exposure photography," said Battams. "It's possible that
if we doubled exposure time again, we'd see even more comets." SOHO is
a cooperative effort between ESA and NASA. Mission control is based at
NASA's Goddard Space Flight Center in Greenbelt, Maryland. SOHO's Large
Angle and Spectrometric Coronagraph Experiment, or LASCO, which is the instrument that provides most of the comet imagery, was built by an international consortium, led by the U.S. Naval Research Lab.


========================================================================== Story Source: Materials provided
by NASA/Goddard_Space_Flight_Center. Original written by Sarah
Frazier. Note: Content may be edited for style and length.


==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/06/200617121504.htm

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