It's difficult for us humans to fully
comprehend the enormity of space. We are
comfortable in our own cosmic
neighborhood, the solar system, and are
used to familiar faces like Jupiter,
Mars, and of course, Earth. But out
there, over 18 billion km away from the
sun and beyond the helopor is the cold
oblivion of interstellar space. The two
Voyager probes are the only man-made
objects ever to cross this threshold to
this day. And until recently, only two
known objects have ever made the
opposite journey, passing from
interstellar space into the solar
system. These were the famous Amua Mua
in 2017 and Borisovv in 2019, which
brought with them the thrill and perhaps
even fear of being visited by something
from the depths of space that humans
cannot hope to reach in our lifetimes.
In the 6 years since these visits, we've
been enjoying some restbite, but a
recent observation has forced us to sit
up and pay attention once more. I'm Alex
Mccoan and you're watching Astramm. Join
me in this video as we explore all there
is to know about NASA's latest
observations of comet 3i Atlas, the
third interstellar object ever observed,
which will make its closest approach to
our sun before the year is out.
Thei Atlas has had a few different names
in the short time we've been aware of
it, but recent revelations about where
this object came from and where it is
heading turned this otherwise
indistinguishable space rock into
something worth taking note of. On the
1st of July this year, the NASA funded
Atlas Survey Telescope was performing
its usual task of scanning the skies
above for moving objects. The Atlas
Project or Asteroid Terrestrial Impact
Last Alert System consists of four
telescopes across Chile, South Africa,
and Hawaii. These telescopes each take
around 800 images every night. And at
the time of writing, they have
registered 1,212
near Earth objects that will pass within
1.3 astronomical units of our planet at
Perihelion.
But on this particular night, the
telescope in Rioardo, Chile, reported
some newsworthy observations.
The Atlas telescopes are rather unique
for their ability to survey the galactic
plane, the bright discshaped region of
our galaxy where most of its mass lies.
See, other surveys like Pan Stars and
the Catalina Sky Survey are often too
sensitive to photograph this area
without facing overexposure, so they
tend to avoid it altogether. From the
direction of the Sagittarius
constellation, the Atlas telescope took
four 30-second survey images and found
an object that was making a beline
towards our solar system. The object was
initially named A11 PL3Z
and quickly caught the attention of the
Minor Planet Center in Cambridge,
Massachusetts. As the designated
authority in charge of labeling and
tracking minor bodies in the solar
system, the MPC quickly put out an
electronic circular about this new
visitor, detailing all of its previous
observations and providing information
about its trajectory. In doing so,
astronomers realized that in fact this
object was no stranger to us. As it
turned out, the Zviki Transit Facility
in California and the other three the
three Atlas telescopes had all made
pre-discovery observations of this
object dating back as far as the 14th of
June. With all of this data, the MPC
deduced that the object had a hyperbolic
and highly eccentric orbit. So much so
that it had originated from interstellar
space. This realization earned the
object the name of three atlas as it is
the third interstellar object to
infiltrate our solar system. At first,
the NPC could not be certain whether
this object was an asteroid or a comet
until the combined data revealed that it
had a coma, a diffused halo of dust and
gas produced when ice is exposed to
solar radiation and sublimates. This
feature is far more typical of comets,
which gave this object yet another name,
C2025N1.
The NBC has called for additional
observations of this comet to help
constrain its trajectory, so we can
expect a flurry of new data in the
upcoming months, and astronomers are
naturally very excited. Michelle
Banister, an astronomer at the
University of Canterbury in New Zealand,
explained that working on the two
previous visits from interstellar
objects were transformational
opportunities science-wise. So, it's
likely that this visitor will encourage
the same. But what do we already know
about this latest interstellar visitor?
And what do scientists hope it can teach
us in the near future?
Firstly, don't worry because this comet
will pose no threat to Earth. At its
closest approach to our planet, it will
still be around 1.6 astronomical units
away. That's over 600 times further than
the moon is from Earth. So, since we're
able to watch from a safe distance, what
kind of journey will this comet take? As
I mentioned, three Atlas has a highly
eccentric orbit currently measuring at
an E value of around six. For reference,
an eccentricity of zero represents a
perfect circle. And anything above one
is great enough for the object to escape
the gravitational pole of the body it is
orbiting and will move more freely
through space. So with an eccentricity
of six, this comet has one of the most
extreme hyperbolic orbits yet measured,
which may explain how it is able to
travel so far through space to reach us.
What's more surprising is the speed with
which this comet is traveling. Its
current incoming velocity is a rapid 58
km per second.
That's like running the length of 580
football for pitches every second. This
break neck speed makes three Atlas the
fastest traveling interstellar comet we
have ever seen. Amoa and Borisovv had
velocities of just 26 and 32 km/s
respectively resulting from their
differently shaped orbits.
With such a rapid approach, astronomers
were keen to work out exactly where
three Atlas was headed. The current
orbit is heliocentric or centered around
the sun, meaning it is possible for
astronomers to infer its incoming
trajectory before it reaches us. On its
closest approach to the sun on the 30th
of October, the comet will be at a
distance of 1.4 astronomical units,
placing it just inside the orbit of
Mars. In this graph of the comet's
orbit, you can see the asymptoic shape
of its approach as it veers past Mars
and shoots back out into space.
As the graph shows, ThreeI Atlas will
not pass as close to the sun as the
famous Amuam Mua did in 2017 and will
follow a trajectory more similar to
Borisov's.
Once the interstellar nature of this
comet was clear, astronomers employed
the use of other globally distributed
telescopes to better understand it. In
particular, the telescopes from Lascom's
observatory are purpose-built to observe
transient astronomical events, which can
include events like comet outbursts and
other changes in brightness. Using two
0.36 m LCO telescopes based in Hawaii,
astronomers scheduled a 1-hour
observation sequence for three Atlas.
Their goal was to identify a light curve
for the comet and to see whether it
exhibited any rotational variability.
Rotational variability means any kind of
variation in brightness caused by the
comet spinning on its rotational axis.
Maybe it has an irregular shape and
reflects light differently across its
surface or it has active regions that
appear brighter to us when they face
towards Earth. But by monitoring the
changes in brightness over time,
astronomers can identify repeating
patterns which show that the comet has
completed one cycle of rotation.
Using the LCO telescopes, astronomers
identify that the comet has a rotation
period of around 29 hours. Though like
much of the information about three
Atlas, further observations are needed
to constrain this. In a surprise to
astronomers, Threeey Atlas had a much
flatter light curve than a MUA MUA and
exhibited only 0.2 magnitude of
brightness variation throughout the
29-hour period. But despite this minimal
variation in brightness, 3I Atlas is
bright. In fact, it's the brightest
interstellar object we've seen yet. This
comet was pretty faint right up until
the end of May this year when it reached
a magnitude of around 20. But between
then and the comet's discovery by Atlas,
it has promptly increased to between
17.7 and 17.8 magnitude in the Atlas O
band, which records light wavelengths
between 560 and 820 nanome.
Not only is the comet bright, but it is
large. From assumed albido values, the
diameter of its nucleus is estimated at
10 km.
This makes it an order of magnitude
larger than a mua mua and even larger
than Borisov which measured between 1 to
2 km in diameter.
Further observations have also revealed
that threeey atlas shows faint levels of
activity. As I mentioned, the comet has
a marginal coma, which constitutes the
fuzzy glowing halo of dust and gas that
is produced when a cometry eye
sublimates upon exposure to the sun. You
can make it out in the center of this
image shown here as a diffused circle
around the nucleus. The image is
tracking the moving comet, which is why
the surrounding stars appear blurred.
But as well as a coma, Threeey Atlas has
a tail. The NPC reported a tail spanning
three arcsec across the sky at an angle
of around 280°.
This is pretty short, so the tail is
often lost amongst the coma in images of
the comet. As with many modern
scientific discoveries, the advances in
technology and communication mean that
people from around the world can get in
on the excitement. And that is exactly
what is happening for three eye atlas.
Amateur astronomers and experts alike
are contributing their own observations
of the comet. So our state of knowledge
is constantly being updated. For
example, the astronomer telegram is a
forum for space enthusiasts to post
their findings and is being updated
daily with new revelations. Miguel
Alakon and colleagues have helped to
constrain the tail measurements for the
threeey atlas reporting that it extends
across more than 25,000 km. From this
post and others, we can see some really
exciting images of our new visitor. Just
look at these.
We've covered brightness, rotation, and
activity on the comet, but what about
its surface? Well, in this respect,
ThreeI Atlas is similar to its
predecessors. Just like Amoa and
Borisov, ThreeEi Atlas is significantly
redder than the sun and slightly redder
than Dtype asteroids like those from the
outer asteroid belt. Since it is active,
some of this reflected light must be
coming from Thrii Atlas's coma. The same
was observed for Borisov, where the
reflectance of the coma was drowning out
the signal from the nucleus itself. We
should be able to confirm this as the
comet gets closer to us and new
measurements can be made. For example,
back in 2020, astronomers found that
Borisoft was producing dust at a rate of
50 kg/s,
which helped to explain the drowned
nuclear signal.
Finally, the discovery of three Atlas
has allowed astronomers to make another
estimate for just how many interstellar
objects there are out there. In a paper
published shortly after the comet's
discovery, scientists inferred a density
of just 0.001
interstellar objects per cubit
astronomical unit of space. That's far
smaller than the previous estimates made
when we discovered Amuam and Borisov.
This density value is based on the fact
that Atlas has been scanning our skies
for the past 3 years and has only found
one interstellar object so far. But of
course, the density is liable to change
and depends on many other factors. It
could be that Atlas has let some objects
smaller than three Atlas pass by
undetected, or that there is a
particular signal emitted by these
objects that it fails to detect. We're
not really sure, but estimates like
these are no less useful to us, and we
should try to update them whenever we're
given the opportunity.
So, we've explored the information that
we've managed to gather about this comet
so far. But, as we've seen, science is
anything but stagnant, especially when
there is a brand new toy to play with.
So, what are we hoping to learn from
this comet in the near future? And how
can we learn from our previous
interstellar visitors?
Luckily for astronomers studying
three-ey atlas, there are two fairly
recent case studies to draw from. We've
covered both Borisov and Amua Mua before
on this channel, so definitely check out
our previous videos and our AmuA Mua
super cut if you haven't already for
everything you need to know. As we've
already discussed some of the
similarities and differences between
these objects, but how can these
comparisons be explained and what do
they tell us about the origins of these
visitors?
We've touched on one of the major
differences already and that is that
threeey atlas appears to be less active
than Borisoft was. Two I Boris displayed
significant cometry activity as its dust
coma increased in size by around 1% per
day which indicated that it had been
active for around 100 days prior to its
first observations. It also had a longer
tail spanning 140,000 km into space.
Now, it could be that 3i Atlas hasn't
been exposed to the sun enough to begin
water ice sublimation, which would raise
activity levels, but Borisoft entered a
period of strong activity when it was
still 4.5 astronomical units away from
the sun. And three Atlas is already much
closer than that. So, this looks
unlikely.
Regardless, Amua Mura didn't exhibit
high activity levels either. It was a
dense, rocky body with no ice to
sublimate in the glare of the sun, and
it had no coma or tail. Astronomers are
still trying to explain this lack of
activity to this day with recent
hypotheses that it may have been
outgassing volatiles with a low level of
dust production. So, it wasn't picked up
in the observations. But three atlas
does have a coma. So, this explanation
isn't a one-sizefits-all for both
interstellar objects.
With such differing compositions and
activity levels, what does this tell us
about the origins of interstellar
objects? Well, this is still a major
subject of scientific exploration. The
famous oblong shape of a Moamore
generated a buzz around its origins and
theories emerged that it may be a
primordial object shaped by tidal forces
or the fragment of a planet or the
aggregation of several smaller objects.
Boris also caused speculation of its own
as its composition was different from
those typically seen in solar system
comets. It had a higher abundance of
hypervolatile carbon monoxide relative
to water, suggesting that it may have
formed in a carbonrich environment. In
line with this observation, it was
suggested that Boris formed in a red
dwarf star system with cooler average
temperatures, cool enough for carbon
monoxide to condense and be incorporated
into the comet. At the moment, it's
probably still too soon to say what we
will be able to infer about threeey
atlas's origins, but it is active like
Borisov, and as it starts to be heated
by our sun, perhaps we will detect
similar levels of carbon monoxide,
hinting at a shared interstellar origin.
Speculation aside, it is clear that
three eye atlas is a unique interstellar
visitor worthy of our close attention.
Wherever it may be comparable to
Borisovv or Amua Mua, threeey atlas has
other characteristics that place it in a
different class of object altogether.
As a result, we can view this comet as
an exciting opportunity for new
discoveries and eagerly anticipate the
scientific insights it may reveal. After
all, the estimated density for
interstellar objects is low, so who
knows how long we may have to wait to be
visited again.
Now that we've learned a bit about
ThreeI Atlas, it's over to you. You can
keep an eye out for this comet using
groundbased telescopes from around
September until it disappears behind the
sun. After the 30th of October,
perihelion, the comet will reemerge from
behind the sun in early December, ready
for another round of viewing from Earth.
But if you don't have a telescope, don't
worry. You can still get involved in the
comet action as the JPL Horizon's
website has a handy tool to track its
position in space. When I checked back
on the 4th of July, this was its
heliocentric position. So, why not check
for yourself and see how far it has
traveled in the time it took us to
release this video. Let me know what you
find in the comments. In the meantime, I
can't wait to see what else we can learn
from this plucky interstellar traveler.
It has come an awfully long way, beating
the odds to reach us, and I'm sure it
has plenty of cosmic secrets to spill.
the link to this playlist for more
Astramm content. I'll see you next time.