After 16 years, NASA's Spitzer Space Telescope has come to an end of its mission. The infrared

telescope was decommissioned on January 30th, 2020. But during its lifetime, Spitzer opened

a window onto the old, cold, and dusty Universe. Welcome back to Launch Pad, I’m Christian

Ready, your friendly neighborhood astronomer. While it’s always sad to say goodbye to

such an incredible observatory like Spitzer, it’s also a good time to appreciate the

little space telescope that could literally see what others could not. Spitzer was launched

from Cape Canaveral on August 25 2003. It joined the Compton Gamma Ray Observatory,

the Chandra X-Ray Observatory, and the Hubble Space Telescope in NASA’s Great Observatories

program. Combined, these telescopes would give us our clearest look at the Universe

from gamma rays to the infrared part of the spectrum. Stars are generally hot enough to

radiate most of their energy in the visible part of the spectrum. That makes them pretty

easy to see. But most of the stuff in the universe aren’t stars at all, but dust and

gas. This stuff is much cooler so they radiate most of their energy in the infrared. But

sensing the feeble heat of cold dust requires an even colder detector. It’s the same reason

you need a dark viewing site to see the faintest stars. To that end, Spitzer was launched into

a first-of-its-kind Earth-trailing orbit around the Sun. This kept the spacecraft away from

the thermal environment around the Earth and Moon. It was equipped with a heat shield that

doubled as a solar array. And in a really cool innovation, its opposite half was given

a flat-black paint job to radiate heat away from the spacecraft. Kinda like a wood stove.

Spitzer was equipped with an 85-centimeter telescope and three instruments. These instruments

gave Spitzer sensitivity from the near into the far infrared.

But in order to see in the far infrared, Spitzer had to be kept extremely cold. That’s why

it launched with a cryostat of liquid helium. The cryostat cooled the instruments to temperatures

as low as 1.4 Kelvin (roughly -457 degrees Fahrenheit, or -272 degrees Celsius). As the

liquid helium flowed around the instruments, it gradually boiled off, carrying away heat.

The cryostat was designed to operate for a minimum of 2.5 years. It ended up lasting

5 years and 9 months. That’s 130% longer than the given warranty! In that time Spitzer

executed more than 36,000 hours of science observations. That’s equivalent to more

than 12 years of observations from low earth orbit.

The secret to Spitzer’s efficiency was its unobstructed view of the sky. With no planet

in the way, it could point in any direction as long as it kept its solar arrays toward

the Sun. The Hubble Space Telescope by contrast is in low-Earth orbit, so its view of any

given target can be blocked by Earth for up to half of Hubble's orbit.

Even though its coolant ran out by May 2009, Spitzer still had two working detectors in

its IRAC camera. So Spitzer began its “warm” mission at a balmy -404 degrees Fahrenheit

(-242 Celsius).

Over its 16-year mission, Spitzer revealed more about the cold and dusty universe than

all of the other infrared missions that came before it.

For example, Spitzer discovered the largest ring around Saturn, and it was hiding right

there in plain sight.

Most of Saturn’s rings are close to the planet and are maintained by its inner moons.

But this new ring is much farther and is associated with Saturn’s outer moons, most of which

are captured asteroids. In fact, the ring seems to line up well with Saturn’s largest

outer moon Pheobe.

It’s thought that meteoroid impacts on Pheobe can kick off enough dust to create the ring.

Because these dust particles are dark, they don’t reflect sunlight so much as absorb

it. This causes the dust to heat up, making them very bright in the infrared. Spitzer

captured an edge-on view of a portion of the ring.

The ring explains the strange appearance of Saturn’s moon Iapetus. Iapetus is tidally

locked to Saturn, so one side always faces the planet at all times. Even though its surface

is water ice, one side is covered by a large dark feature that faces into the direction

of its orbit. This led astronomers to wonder if the moon was sweeping up some dark material

as it orbits Saturn. That led to the search for the great dust ring, which Spitzer easily

found. This is the largest ring of Saturn ever discovered and the largest ring in the

solar system. It's one planetary ring to rule them all. Okay, fine, sorry.

Now all of this was possible because dust radiates at far infrared wavelengths. But

mid-infrared wavelengths are just long enough to avoid fine dust particles. This allows

Spitzer to see through the dust that enshrouds young stars forming in their stellar cocoons.

One example is NGC 6334, known as the Cat’s Paw Nebula. It’s a vast region of star formation

shown here in visible light. The red color comes from hydrogen gas energized by hot stars

in the nebula.

But at infrared, the image is completely different. Instead of the hot gas, red now indicates

the cool, darker dust. Notice that we can now even see stars that were otherwise blocked

by the dust. If we include information from the far infrared, the dust that’s being

warmed up by the stars inside now becomes visible. This kind of analysis allows astronomers

to reveal where in the nebula stars are forming. And even then, there are some regions that

are so thick with dust they still appear dark at infrared wavelengths.

Spitzer taught us a lot about extrasolar planets, which is remarkable because extrasolar weren’t

even a thing when the mission was designed. Nevertheless, it produced the first-ever weather

map of a planet beyond our solar system. The planet in question is HD 189733b. Spitzer

measured the infrared light coming from the planet as it circled around its star. The

hot spot on the planet confirms that it's tidally locked to its star. However, the planet's

overall temperature variation is relatively mild. This suggests that winds are spreading

the heat from its day side around to its dark side. Such winds might rage across the surface

at up to 6,000 miles per hour (9600 kph). How cool is that? The first exo-weather report!

But Spitzer’s most dramatic exoplanet result was its look at the TRAPPIST-1 system. After

monitoring the system for 500 hours, Spitzer revealed that TRAPPIST-1 is home to seven,

count ‘em SEVEN Earth-sized planets surrounding the red dwarf star! And if that weren’t

amazing enough, at least 3 of those planets orbit in the star’s “habitable zone”.

Scientists used Spitzer to characterize Brown Dwarfs. These are objects that fall somewhere

between failed stars and highly successful planets. In a 2014 study, astronomers discovered

that brown dwarfs typically have atmospheric storms.

As a brown dwarf rotates, its clouds move in and out Spitzer’s line of sight, causing

changes in its infrared brightness. Astronomers analyzed these brightness variations to determine

how clouds are distributed in brown dwarfs. With the help of some supercomputer modeling,

they showed how large atmospheric waves could combine to form bright spots in the atmosphere

and separate to produce darker regions.

Over the course of a decade, Spitzer devoted a total of 172 days taking images of the disk

of our Galaxy. The project was the Galactic Legacy Mid-Plane Survey Extraordinaire or

GLIMPSE. In 2014, astronomers completed the painstaking work of stitching together each

of the images into the largest infrared panorama of our home Galaxy.

This picture covers only about 3% of the sky, but includes more than half of the galaxy's

stars and the majority of its star formation activity.

The red color shows dusty areas of star formation. Massive stars blast out winds and radiation,

and sculpt giant bubbles and plowing mountains of dust. Elsewhere, clusters of gestating

stars deep in cocoons of gas and dust are revealed.

Spitzer uncovered whole galaxies to reveal their structure. M81 is a relatively nearby

galaxy. Hubble gives us our clearest visible light image, but Spitzer is able to selectively

image the starlight at 3.6 and 4.5 microns. This shows the distribution of stars throughout

the galaxy. But if we view the galaxy at 8 microns, we see the glow of the dust resembling

a galactic skeleton. Combining these two images gives us an infrared map of the galaxy and

if include the 24 micron channel, we see where new stars are forming in the spiral arms.

It was an incredible run for Spitzer, but its unique vantage point away from Earth meant

it wouldn’t be able to be operated indefinitely.

In order to downlink its data and receive new commands, Spitzer must point its high-gain

antenna toward Earth. Early on in the mission, Spitzer could perform this maneuver while

still keeping its heat shield toward the Sun.

But over time, as Spitzer continued to drift farther away from Earth, so it had to tilt

farther away from the Sun to communicate with Earth. Not only that but it had to maintain

this pointing for longer periods as the light travel time between Earth and Spitzer increased.

Throughout its mission, NASA conducted periodic reviews to assess Spitzer. This is a common

practice as NASA has a habit of building spacecraft that last way longer than they’re supposed

to.

Anyway, these reviews often result in mission extensions. Since the James Webb Space Telescope

is an infrared observatory, NASA announced in 2016 that Spitzer would be decommissioned

in 2018, which at the time was when JWST was supposed to launch.

However, when JWST’s launch was postponed to 2021, NASA announced a final extension

of the Spitzer mission, called Spitzer Beyond.

The name was appropriate. Not only was Spitzer operating well beyond its original lifetime,

but it would have to operate Spitzer way beyond its design limits.

During normal science operations, Spitzer could aim up to 30 degrees away from perpendicular

to the Sun. Any further and Spitzer’s heat shield would no longer protect the spacecraft.

In fact, Spitzer had onboard fault protection software to prevent the telescope from pointing

beyond this limit.

During the Beyond mission, engineers would disable the fault protection to allow Spitzer

to point way past this limit during data downlink. This was incredibly risky, because solar array

couldn’t provide power and the spacecraft so it would need to rely on batteries. But

the exposure to sunlight would raise the temperature of the high gain antenna and struts. That

heat would work its way up to the rest of the spacecraft.

Still, the maneuver worked. So it’s natural to wonder why not just continue to use Spitzer

until it breaks? The answer ultimately comes down to funding. NASA’s budget is roughly

one half of one percent of the federal budget and there are new missions coming. Not the

least of which are the James Webb Space Telescope, which, again, will hopefully launch in 2021

(although we’ll see) and the Wide-Field Infrared Survey Telescope or WFIRST which

will hopefully launch later this decade.

JWST in particular is much larger and more sensitive than Spitzer and now that it looks

like it's going to launch within our lifetimes, the decision was made to bring the Spitzer

mission to a responsible end.

On January 30th, spacecraft operators issued their final command to put Spitzer into “safe

mode”. This mode powers down all non-essential systems and orients the solar panels toward

the Sun.

Safe mode keeps the spacecraft in a powered hibernation state while waiting for a recovery

command from Earth. Only in this case, no such command will ever be sent. Spitzer will

remain in its Sun coning attitude, sleeping in its orbit around the Sun.

It will continue to drift farther away from Earth, until it reaches a maximum distance.

After which, Earth will begin to catch up and eventually lap Spitzer in its orbit around

the Sun. This will occur sometime around the year 2056, 53 years after it launched.

This will send Spitzer into a slightly closer orbit to the Sun and speed up, until it comes

around and laps past Earth once again. Only this time, it will be boosted into a more

distant orbit around the Sun. It’s neat to think that Sptizer’s always going to

be out there, somewhere and who knows, maybe in a few hundred years our descendants will

go out there, pick it up and put it in a museum. It would be a fitting tribute to our early

glimpses into the cold, dusty universe.

So what’s your favorite Spitzer result? Let me know in the comments below and I'll

be sure to check them out. And, I’d like to thank my Patreon supporters for helping

to keep this channel going, and I’d like to welcome my newest patrons, Dave Mausner,

Andy Law, and a special welcome my newest Cosmological supporter, Michael Dowling along

with, once again, to Steven J. Morgan. If you’d like to help support Launch Pad for

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Until next time, stay curious, my friends.