Asteroid's comet-like tail Is not made of dust, solar observatories
reveal
Date:
April 25, 2023
Source:
NASA/Goddard Space Flight Center
Summary:
We have known for a while that asteroid 3200 Phaethon acts like
a comet.
It brightens and forms a tail when it's near the Sun, and it is
the source of the annual Geminid meteor shower, even though comets
are responsible for most meteor showers. Scientists had blamed
Phaethon's comet-like behavior on dust escaping from the asteroid
as it's scorched by the Sun. However, a new study using two NASA
solar observatories reveals that Phaethon's tail is not dusty at
all but is actually made of sodium gas.
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==========================================================================
FULL STORY ==========================================================================
A weird asteroid has just gotten a little weirder.
We have known for a while that asteroid 3200 Phaethon acts like a
comet. It brightens and forms a tail when it's near the Sun, and it is
the source of the annual Geminid meteor shower, even though comets are responsible for most meteor showers. Scientists had blamed Phaethon's comet-like behavior on dust escaping from the asteroid as it's scorched
by the Sun. However, a new study using two NASA solar observatories
reveals that Phaethon's tail is not dusty at all but is actually made
of sodium gas.
"Our analysis shows that Phaethon's comet-like activity cannot be
explained by any kind of dust," said California Institute of Technology
PhD student Qicheng Zhang, who is the lead author of a paper published
in the Planetary Science Journal reporting the results.
Asteroids, which are mostly rocky, do not usually form tails when
they approach the Sun. Comets, however, are a mix of ice and rock,
and typically do form tails as the Sun vaporizes their ice, blasting
material off their surfaces and leaving a trail along their orbits. When
Earth passes through a debris trail, those cometary bits burn up in our atmosphere and produce a swarm of shooting stars -- a meteor shower.
After astronomers discovered Phaethon in 1983, they realized that the asteroid's orbit matched that of the Geminid meteors. This pointed to
Phaethon as the source of the annual meteor shower, even though Phaethon
was an asteroid and not a comet.
In 2009, NASA's Solar Terrestrial Relations Observatory (STEREO)
spotted a short tail extending from Phaethon as the asteroid reached
its closest point to the Sun (or "perihelion") along its 524-day
orbit. Regular telescopes hadn't seen the tail before because it only
forms when Phaethon is too close to the Sun to observe, except with
solar observatories. STEREO also saw Phaethon's tail develop on later
solar approaches in 2012 and 2016. The tail's appearance supported the
idea that dust was escaping the asteroid's surface when heated by the Sun.
However, in 2018, another solar mission imaged part of the Geminid debris
trail and found a surprise. Observations from NASA's Parker Solar Probe
showed that the trail contained far more material than Phaethon could
possibly shed during its close approaches to the Sun.
Zhang's team wondered whether something else, other than dust, was behind Phaethon's comet-like behavior. "Comets often glow brilliantly by sodium emission when very near the Sun, so we suspected sodium could likewise
serve a key role in Phaethon's brightening," Zhang said.
An earlier study, based on models and lab tests, suggested that the
Sun's intense heat during Phaethon's close solar approaches could indeed vaporize sodium within the asteroid and drive comet-like activity.
Hoping to find out what the tail is really made of, Zhang looked for it
again during Phaethon's latest perihelion in 2022. He used the Solar and Heliospheric Observatory (SOHO) spacecraft -- a joint mission between
NASA and the European Space Agency (ESA) -- which has color filters that
can detect sodium and dust.
Zhang's team also searched archival images from STEREO and SOHO, finding
the tail during 18 of Phaethon's close solar approaches between 1997
and 2022.
In SOHO's observations, the asteroid's tail appeared bright in the filter
that detects sodium, but it did not appear in the filter that detects
dust. In addition, the shape of the tail and the way it brightened as
Phaethon passed the Sun matched exactly what scientists would expect if
it were made of sodium, but not if it were made of dust.
This evidence indicates that Phaethon's tail is made of sodium, not dust.
"Not only do we have a really cool result that kind of upends 14
years of thinking about a well-scrutinized object," said team member
Karl Battams of the Naval Research Laboratory, "but we also did this
using data from two heliophysics spacecraft -- SOHO and STEREO -- that
were not at all intended to study phenomena like this." Zhang and his colleagues now wonder whether some comets discovered by SOHO - - and by
citizen scientists studying SOHO images as part of the Sungrazer Project
-- are not comets at all.
"A lot of those other sunskirting 'comets' may also not be 'comets'
in the usual, icy body sense, but may instead be rocky asteroids like
Phaethon heated up by the Sun," Zhang explained.
Still, one important question remains: If Phaethon doesn't shed much
dust, how does the asteroid supply the material for the Geminid meteor
shower we see each December? Zhang's team suspects that some sort of disruptive event a few thousand years ago -- perhaps a piece of the
asteroid breaking apart under the stresses of Phaethon's rotation --
caused Phaethon to eject the billion tons of material estimated to make
up the Geminid debris stream. But what that event was remains a mystery.
More answers may come from an upcoming Japan Aerospace Exploration Agency (JAXA) mission called DESTINY+ (short for Demonstration and Experiment
of Space Technology for Interplanetary voyage Phaethon fLyby and dUst
Science). Later this decade, the DESTINY+ spacecraft is expected to
fly past Phaethon, imaging its rocky surface and studying any dust that
might exist around this enigmatic asteroid.
* RELATED_TOPICS
o Space_&_Time
# Asteroids,_Comets_and_Meteors # Sun # Solar_Flare #
Astronomy # NASA # Space_Exploration # Space_Missions
# Solar_System
* RELATED_TERMS
o Comet o Asteroid o Comet_Shoemaker-Levy_9 o Comet_Hale-Bopp
o Solar_system o Impact_crater o Asteroid_belt o Meteor
========================================================================== Story Source: Materials provided by
NASA/Goddard_Space_Flight_Center. Original written by Vanessa
Thomas. Note: Content may be edited for style and length.
========================================================================== Related Multimedia:
* Asteroid_Phaethon ========================================================================== Journal Reference:
1. Qicheng Zhang, Karl Battams, Quanzhi Ye, Matthew M. Knight, Carl A.
Schmidt. Sodium Brightening of (3200) Phaethon near Perihelion. The
Planetary Science Journal, 2023; 4 (4): 70 DOI: 10.3847/PSJ/acc866 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2023/04/230425111159.htm
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