Hello Space Fans and welcome to another edition of Space Fan News.
This week, the Hubble Space Telescope takes aim at one of the most studied supernovae
ever: Supernova 1987A on the 30th anniversary of its discovery; the MAVEN orbiter around
Mars performs an unscheduled maneuver to avoid crashing into Phobos; and an update on the
launch date of TESS, the Transiting Exoplanet Survey Satellite.
Thirty years ago, on February 23rd 1987, the first photons arrived at Earth from a core
collapse supernova that occurred in the Tarantula Nebula, located in the Large Magellanic Cloud
some 168 thousand light years away.
This was the closest observed supernova since the invention of the telescope and it set
the astronomical community on fire.
Supernova 1987A was so bright that it could be seen from the southern hemisphere with
the naked eye.
After fading some four days later, it was found that the supernova came from a blue
supergiant star and while it was very bright, it was only about one tenth as bright as other
supernovae from blue supergiants.
Without a doubt, because it was detected early and was so close, this has been the most studied
supernova in history and it revolutionized our understanding of the deaths of massive
stars.
Before this event, our observations were spotty and our models were simplistic, but that all
changed when astronomers were able to study this explosion from beginning to end.
So in 2017 astronomers now have 30 years of observations of this supernova and the Hubble
Space Telescope has looked at it many times over the last 27 years.
Remember, Hubble was launched in 1990, three years after it happened.
Well in celebration of the 30th anniversary, in January 2017, Hubble took another look
at the supernova and the Space Telescope Science Institute assembled all of the Hubble observations
into a really cool time lapse that shows how the stellar remnant has evolved in a level
of detail that only Hubble can provide.
Back in 1990, Hubble was the first to see the event in high resolution, clearly imaging
the main ring that blazes around the exploded star.
It also discovered the two fainter outer rings, which extend like mirror images in a hourglass-shaped
structure.
Even today, they don’t know where these structures come from.
However, by observing the expanding remnant material over the years, Hubble helped to
show that the stuff inside this structure was ejected 20 000 years before the actual
explosion took place.
Its shape kinda surprised astronomers, they were expecting to see the dying star eject
material in a spherical shape — but faster stellar winds prior to the explosion likely
caused the slower material to pile up into ring-like structures.
The initial burst of light from the supernova lit up the rings.
Then they slowly faded over the first decade after the explosion, until the shock wave
of the supernova slammed into the inner ring in 2001, heating the gas to searing temperatures
and generating strong X-ray emission.
Hubble’s observations of this process shed light on how supernovae can affect the dynamics
and chemistry of their surrounding environment, and thus shape galactic evolution.
What I think is cool about this story is that about 2 to 3 hours before the visible light
photons reached Earth, a burst of neutrinos was observed at three separate neutrino observatories
around the world.
This was likely due to neutrino emission, which occurs at the same time as the core
collapse, but preceds the emission of visible light.
A strange thing about SN 1987A is that while it appears to be a core-collapse supernova,
no one has found the neutron star which should have been left behind.
The neutrino data indicate that a compact object did form at the star's core.
but, since the supernova first became visible, astronomers have been searching for the collapsed
core but have not detected it, not even with Hubble.
As you can imagine, there are lots of theories about why they haven’t seen it.
The first is that the neutron star is hidden in dense dust clouds so that it can’t be
seen.
Another is that a pulsar was formed, but with either an unusually large or small magnetic
field.
It is also possible that large amounts of material fell back on the neutron star, so
that it further collapsed into a black hole.
As you guys all know by now, both neutron stars and black holes often give off light
when material falls onto them.
If there is a compact object in the supernova remnant, but no material to fall onto it,
it would be very dim and could therefore be why we haven’t seen it.
Next, NASA’s MAVEN orbiter over Mars had to make an unscheduled change in course to
avoid running into one of Mars’ two moons: Phobos.
The MAVEN spacecraft has been orbiting Mars for just over two years, studying the Red
Planet's upper atmosphere, ionosphere and interactions with the sun and solar wind.
On Tuesday, Feb. 28, the spacecraft carried out a rocket motor burn that boosted its velocity
by 0.4 meters per second (less than 1 mile per hour).
A small correction, but it was enough that, had they done nothing it would have probably
hit Phobos about one week later.
With this new correction, MAVEN will miss the lumpy, crater-filled moon by about 2.5
minutes and according to NASA this is the first collision avoidance maneuver that the
MAVEN has performed at Mars to steer clear of Phobos.
The orbits of both MAVEN and Phobos are known well enough that this timing difference maneuver
makes sure that they will not collide.
For a while there, with only one week's advance notice, it looked like MAVEN and Phobos had
a good chance of hitting each other this coming Monday, March 6, arriving at their orbit crossing
point within about 7 seconds of each other.
Given Phobos' size, they had a high probability of colliding if no action were taken.
So NASA made the adjustment and it looks like all is well.
BTW, as a side note, coincidentally we held our monthly Footsteps to Mars hangout yesterday
where our guest, Dr. Pascal Lee gave a really good discussion of the moons of Mars, Phobos
and Deimos so check it out if you want to learn more about these bodies.
I also learned in that hangout yesterday that the IAU are working on a new definition of
a planet that will make Pluto a planet again.
Finally, I wanted to update you on the launch date of TESS, the Transiting Exoplanet Survey
Satellite.
It was originally scheduled to launch this August, but the date has been pushed back
to next year.
According to NASA, the launch of TESS will occur no later than June 2018 and they are
shooting for March 2018.
If you want to learn more about TESS, check out the video I made last year on it.
Everything else is still accurate on the video, except the launch date.
Well that’s it for this week Space Fans, this show is made possible by support from
SFN Patreon Patrons, without their help, this doesn’t happen so thank you all.
Thanks to all of you for watching and as always, Keep Looking Up!