The James Webb Telescope has arrived and is about to get to work!
After twenty years of planning and thirty days in space, the James Webb Telescope has
finally arrived at its destination.
After opening slowly in the previous days, like a colorful flower in the desert, Monday,
January 24 the giant instrument is positioned in the workplace that will occupy the next
10 or 15 years.
A workplace very distant from Earth, a tiny oasis of gravitational tranquility where other
probes have already taken place over time…
We are talking about the now famous Lagrange Point L2, and we are sure you’ve heard of
it before.
In the three-body problem, which consists in calculating the position and velocity of
three celestial bodies subject to the influence of mutual gravitational attraction, the Lagrange
points (named after the Italian mathematician Giuseppe de Lagrange, who in 1772 calculated
their number and position), are five points in space where two bodies with large mass
(in this case Sun and Earth), allow a third body with much lower mass (in this case the
Webb Telescope) to maintain a stable position relative to them.
So in a planetary system (star with planets) a small object, such as a satellite or an
asteroid, sharing the same orbit of a planet and positioned in a Lagrange point, will maintain
a constant distance from the star and the planet with which it shares the orbit.
Although all Lagrange points are points of gravitational equilibrium, not all of them
are completely stable.
L4 and L5 (the ones that are occupied by the Trojan asteroids in the Sun-Jupiter system)
are much more so than L1, L2, and L3; so that in L2 Webb will not occupy a fixed place but
will orbit around an equilibrium point and its orbit will have to be continuously adjusted
by the on-board thrusters.
At this point, we could also ask: but why make him go so far when instead Hubble did
its job very well from only 400 km high?
Simple.
Webb is a telescope designed to see in the infrared, that part of the spectrum where
light travels on long waves and at a lower frequency, suitable to "drill" the clouds
of gas and dust and see what is hidden behind.
In addition, since the universe is constantly expanding, the light of the bodies that come
to us from millions or billions of light years also tends to move to lower frequencies (redshift
phenomenon).
These objects are therefore more easily detectable if observed with instruments optimized for
the study of infrared frequencies.
To do this, however, it is necessary to operate at very low temperatures to avoid any thermal
interference, being the infrared very sensitive to heat...
And the working place in L2 - in fact - allows Webb to operate leaving the Sun, the Earth,
and the Moon permanently behind him, protected by the specially designed heat shield.
Note that it is simpler, easier, and more efficient to orbit around L2 than to dwell
precisely at L2.
Furthermore, by orbiting rather than being exactly at L2, Webb will never have the Sun
eclipsed by Earth, which is necessary for Webb's thermal stability and power generation.
In fact, Webb's orbit around L2 is larger than the Moon's orbit around Earth!
For the rest of its operational life, Webb will orbit L2 at distances between 248,000
and 820,000 kilometers, taking six months to complete an orbit.
Because the orbit around L2 is not perfectly stable, small thrusters will be activated
every three weeks or so to maintain the telescope's trajectory.
As of Saturday, January 22, the mirror segments had cooled to about -170°C, on track for
an operating temperature of about 50° above absolute zero.
As the cooling process progressed, on Monday, January 24 at 2:00 p.m. EST there was the
planned course correction, with the thrusters fired for 4 minutes and 58 seconds to increase
the spacecraft's speed by 5.5 km per hour: just enough to put it into an orbit around
the L2 point.
Now the Webb Telescope is in this remote region, 1.5 million kilometers away... 1.1 million
kilometers beyond the Moon's orbit.
In the company of other probes such as ESA's GAIA Space Observatory, which arrived here
in 2013, and the Russian-German high-energy astrophysics space observatory, which arrived
in 2019.
In the past, historical probes such as the Herschel Space Observatory and Planck, both
from 2009 to 2013, have "lived" here, before being diverted at the end of the mission on
a heliocentric orbit (to not clog too much the traffic of the area).
And here in the future will be sent the large space telescopes in design, such as the already
legendary LUVOIR.
So the Webb Telescope will be in good company!
And with this, we can declare closed, with a happy ending, a scientific and technological
odyssey lasted over 20 years: the Webb Telescope is finally in position, and everything is
fully functional!
Functioning, yes, but not yet fully operational!
Scientists and engineers now must transform the $10 billion instrument into a working
telescope, precisely aligning its 18 primary mirror segments so that they work together
as a single 6.5-meter mirror, by far the largest ever launched.
If Webb were pointed at a bright star today, we wouldn't get a single image, but 18 individual,
very blurry images.
It would be like having 18 separate telescopes.
In fact, the hexagonal mirrors that make up the primary mirror are currently misaligned
and do not all focus on the same focal point.
Alignment operations will occur between the 33rd and 90th day after launch.
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These corrections are made through a process called wavefront sensing and control, which
aligns the mirrors with the precision of a few tens of nanometers (about 1/10,000 millimeters)
and the motion is controlled through the six actuators mounted on the back of each hexagon.
A seventh actuator can push or pull the center of a segment to slightly distort its curvature,
if necessary.
This will be the next big hurdle for the Webb team: mapping and then skewing each segment
in small increments so that the 18 images end up merging a single, exactly focused point
of light.
It's a multi-step iterative process that should take several months to complete.
It's estimated that the first useful image taken by Webb will arrive toward the end of
the third month after launch, but that's a very tentative date.
And in any case, that still won't be enough for science observations to begin.
Once the optical system is aligned, the team will need to focus on testing and calibrating
the instruments, which will take another two months or so to complete.
Only then will the focused images of the "first light" be released to the public.
And at this point, the question that arises is: what, the Webb Space Telescope will focus
its attention on to celebrate the "first light"?
When you spend $10 billion on a space telescope, you have to justify it to tax-paying citizens.
And that's part of the reason it's become something of a tradition for astronomers to
celebrate the start of a telescope's operation with a selection of images, to show exactly
what it can do and how taxpayer money was well spent.
Not only that.
It will of course also be an opportunity to test the onboard instrumentation on diffuse
and uniformly bright objects, a necessary condition for instrument calibration.
For this reason, many astronomers are betting that the choice will fall on objects that
are part of the Large Magellanic Cloud, the famous dwarf galaxy that orbits our Milky
Way at a distance of 170,000 light years.
The Large Magellanic Cloud and the nearby Small Magellanic Cloud are dense stellar fields
that appear to the naked eye as fuzzy spots.
Although they are both circumpolar, they are best seen from equatorial regions and the
southern hemisphere when they are highest in the sky on a dark, moonless night between
September and April.
They lie between the stars Canopus and Achernar and are named after the Portuguese explorer
Ferdinand Magellan, who spotted them in 1519 during his circumnavigation of the globe.
It is said that, apart from its photometric characteristics, the Large Cloud may have
already been chosen - when the exact launch date was not yet known - for its observability
at any time of the year.
The small galaxy is in fact close not only to the celestial south pole but also to the
bright center of the Milky Way.
And it is also full of incredible astronomical targets, such as the famous Tarantula Nebula.
But then, when will we see the first images demonstrating Webb's photographic capabilities?
Well, my best guess is the last week of May 2022.
Also, the images will have to be first calibrated, cleaned of artifacts, and processed in false
colors.
Once this last hurdle is overcome, we will finally enter the purely scientific phase
of the mission.
We know that over the years, Webb will photograph the early galaxies, explore the mysteries
of the universe’s origins, and see the exoplanets directly...
but, exactly, what are the observations that he will begin to make in the first months
of activity?
Let's find out in the course of this short roundup!
The biggest project of the first year will be COSMOS-Webb, a survey conducted with the
Near-Infrared Camera in a celestial field of 0.6 square degrees already explored by
Hubble.
During the approximately 210 hours of observations, Webb will try to complete the ambitious project
to observe half a million galaxies in the near-infrared, high-resolution, and 32,000
galaxies in the mid-infrared: a number unprecedented to date.
With such a large area, equal to that of three full moons, Webb will be able to go back in
time to highlight large-scale structures dating back to the formation of the first galaxies.
And, by exploiting light distortions around galaxies due to gravity, he may be able to
estimate the amount of "dark matter" inside them.
Overall, COSMOS-Webb will become a collection of data destined to revolutionize cosmology.
A sort of bible for all scholars of the universe.
Meanwhile, Webb will point his big eye on TRAPPIST-1, a small and faint red dwarf located
in Aquarius, about 41 light years away from the Sun; a star around which seven planets
the size of our Earth have been found.
Webb will have to tell us if these planets possess their atmosphere and if they are compatible
with the emergence of life.
And how do stars and star clusters form?
One would think that astronomers would know by now, but unfortunately, much of the universe
is obscured by gas and dust, and this prevents us from having a correct view of the real
mechanisms at stake.
So that Webb will try to answer that, too, thanks to his infrared sensitivity.
An international research team will examine the stars, star clusters, and dust found within
19 nearby galaxies, trying to reveal star formation in its earliest stages, just when
the gas collapses to form stars and heats the surrounding dust.
And this survey will also forever change our view of the universe.
What about the Solar System?
Yes, that's also on Webb's agenda for the first few months of operation!
And in this particular case, the super telescope will deal with Uranus and its satellites.
Aside from a brief flyover in 1986 by the Voyager 2 probe, the seventh planet from the
Sun is in fact still virtually unexplored, and its 27 moons even more so.
And that’s where Webb comes in.
The telescope will in fact have 21 hours of its time to study Ariel, Umbriel, Titania,
and Oberon, the largest moons of Uranus; moons that will be examined to find traces of ammonia,
organic molecules, carbon dioxide, ice, and water; and to confirm or deny the presence
of underground oceans.
And finally, black holes could certainly not miss in the carnet 2022 of the great space
telescope!
Astronomers have long found at the center of a nearby galaxy called NGC 4151 a supermassive
black hole, heavy 40 million times our Sun.
Well, in an attempt to understand exactly how the black hole interacts with the surrounding
matter, a team led by the University of Memphis will use Webb to determine with extreme precision
how the movements of stars near the core of the galaxy vary over time.
Something that until now had been done for the center of our Galaxy by Hubble and ground-based
telescopes, but with much approximation.
Instead, Webb will also show us how the motion of those stars will increase as the mass of
the black hole increases...
In short, a lot of good things are coming from space in 2022; especially from that little
slice of sky, we call Lagrange L2.
But speaking of which...
could we physically see it here from Earth, the James Webb Telescope?
No, it would require very powerful telescopes, but in the nighttime hours, it will be possible
to identify quite easily the point in the sky where it is orbiting, which will be the
one exactly opposite the Sun.
On the evening of February 6, for example, the Telescope will be in Canis Minor, very
close to Procyon, the main star of that constellation.
If you try to find him, say hello to him for me too!