Expected Space Telescope Discoveries

By Robert Bernstein

Our latest Humanist Society talk explored the latest round of understanding the universe through space observations. Humanist Society President Judy Flattery reviewed why this relates to Humanism:

Full disclosure: Exploring and understanding the wonders of our universe sits at the top of my list of what gives meaning to life.

UCSB Physics Professor Roger Freedman held our attention as he explained the wonders and understanding that the James Web Space Telescope (JWST) will give us. I will add that we are grateful that Professor Freedman is allowing us to share his slides here.

The JWST launched 25 December 2021 after many expected launch dates going back to 2016.

Freedman showed us NASA’s concept for the “Next Generation Space Telescope” in 1989. Notably, while Star Trek: The Next Generation was still being made!

He showed the scale of this massive scientific instrument with a photo of a full scale model surrounded by a crowd of people. The mirror is 24 feet across. The largest telescope ever placed in orbit.And this is no ordinary orbit. We usually think of low Earth orbit for such instruments as the Hubble Space Telescope (HST). The HST orbits at just 340 miles above the Earth. It was placed in orbit by the Space Shuttle Discovery in 1990 and has been serviced by five Space Shuttle missions.

In contrast, the JWST is at a point in space called Lagrange Point 2 (L2 for short) about 930,000 miles from Earth! Over 4 times the distance to the moon!L2 lies beyond the Earth’s orbit around the Sun. Objects at L2 orbit the Sun while the gravitational pull of the Earth keeps it at a constant distance from the Earth. The JWST actually orbits this L2 point. Orbital mechanics is an application of the basic physics of Newton, but it is full of wonderful surprises! This orbital space is big enough that it is not at risk of hitting other spacecraft or other objects near L2.

Why have it so far away? At this distance, no spacecraft could get there to service it. One side of the JWST will always face the Sun and will be at the toasty temperature of 185 degrees Fahrenheit. Its cold side will be at the frigid temperature of minus 388 degrees Fahrenheit. Colder than liquid nitrogen. All of the instruments are located on this cold side.

In a word: “Infrared”. Visible light spans the spectrum of wavelengths from 0.4 to 0.8 microns. Infrared has a longer wavelength. Oven heaters put out infrared. Infrared is heat radiation. The JWST can “see” in the range of 0.6 to 28 microns.

To be able to see what it is looking for, the JWST has to be shielded from heat as much as possible. Orbiting L2 keeps both sides of the JWST at a stable temperature.

Freedman showed us how you can see a man’s arm inside a black plastic trash bag using infrared. Infrared can pass through material that blocks visible light. Including dust and certain gases in space.

He noted that some materials that are transparent to visible light will block infrared. This includes glass and the Earth’s atmosphere.

This is what causes the “greenhouse effect” that keeps the Earth warm: Visible light passes right through the atmosphere and heats the Earth. This heat is re-emitted as infrared, but is blocked by the atmosphere, trapping the heat as if the atmosphere were a blanket.

(This greenhouse effect is also what is causing the Climate Crisis as more carbon in the atmosphere increases this effect.)

This also explains why an infrared telescope needs to be placed above the atmosphere.

Herschel and Spitzer were previous infrared telescopes that were in orbit. Because they were in low Earth orbit, they needed to be refrigerated with helium. That refrigerant eventually ran out. Some data could be taken for another 15 years, but it was not suitable for many purposes.

Due to its location, the JWST is cooled passively with a giant shade structure. This shield is the size of a tennis court! It has five layers with gaps in between. It is the equivalent of SPF 1000 sun block!

The shield is made of Kapton polyimide film. It is light weight and folds well. And it is very reflective.

The structure is very complex and had to unfold in many stages. I personally was concerned that such a complex mechanism might not work. Did I mention there would be no way to go out there and fix it if it did not unfold properly? And that would effectively end the mission? I am very happy that I was wrong and that it unfurled perfectly!

The JWST has some propellant to make minor adjustments to its position. But its position around L2 keeps its orbit quite stable.

The JWST 24 foot mirror is actually made of 18 adjustable mirror segments. A bigger mirror gathers more light from faint objects. And it gives sharper images. The Hubble Space Telescope had a single mirror that was made with a slightly incorrect curvature. That had to be repaired later in a risky mission.

The JWST’s 18 mirror segments being adjustable means any such problems can be fixed later. Did I mention it is really far away and can’t be visited by repair astronauts? Using 18 segments also allowed each segment to be optimized during manufacturing.

This mirror is actually the “primary mirror”. Light from this mirror hits a secondary mirror on a boom which then directs the light to the instruments.

The resolution of this precision instrument is equivalent to seeing a penny 40km away!

The JWST has been up for almost six months, but the science has not yet begun.

What will we learn from the JWST? It can see through the gas and dust of regions where stars are forming. Freedman compared it to viewing a baby with ultrasound.

He showed an image of the Carina Nebula 7500 light years away, which is just such a “star nursery”.

The JWST can also look for Earth-like planets. He showed the TRAPPIST-1 planetary system 40 light years away. These planets orbit so close to their sun that they are all closer than Mercury is to our Sun. But that sun is dimmer than ours. Such that four of these planets are in the “Goldilocks Zone” where life as we know it could survive.

Even more valuable: The JWST can look at light from a star passing through the atmosphere of a planet. Which gives a spectrum of the atmosphere. Which gives clues about what that atmosphere is made of and if it contains materials created by living things.

The JWST can also look for planet formation around stars. He showed us HL Tauri which is just 100,000 years old and 450 light years away. It looks like a disc. Similar to how our solar system was at the time our planets were forming.

Finally, the JWST will be able to look far out in space, meaning far back in time. This, because light from far away started out long ago. The JWST will be able to look back to 100 million to 250 million years after the Big Bang. A time when the first stars and galaxies were forming.

We don’t have those pictures yet, but JWST should give them to us in the coming years!

HSSB President Judy Flattery kicked off the Questions asking if the hexagonal segmented mirror introduces distortion. Freedman compared it to covering half of a shaving mirror. It dims the image, but introduces no distortion.

He said the mirror is made of beryllium which is very light weight and very reflective to infrared. And also very toxic!

Judy added that she and husband Dave once worked at the Kapton factory. She went on to ask about universal expansion. Can objects separate faster than light?

Freedman said the rate of expansion has changed over time. For awhile the expansion was slowing, as might be expected due to gravity. But the mysterious “dark energy” seems to cause accelerating expansion now.

Yes, objects can separate faster than light if far away from each other in the universe. This is OK as long as they cannot communicate faster than light.

Freedman said that the frame of reference used for the entire universe is actually the Earth’s north and south poles! This axis slowly drifts and gets updated every few decades.

Yes, there is background noise. This is subtracted out using a dark exposure as a reference.

Star Trek or Star Wars? Freedman likes both. As a kid in the 60s he even watched Lost in Space. There weren’t many choices. Now there are many.

Wayne asked if the Kapton is covered in gold? Actually, it is aluminized.

Donna wanted to know when we will see images. Freedman explained that astronomers put in viewing requests and take data. But then grad students do the tedious analysis work. The results are embargoed to get papers out and to get proper credit.

There are no standard “false colors” for infrared images. JWST images may create a new standard.

Gordon noted that an accurate launch gives added life to the mission as fewer propellants are needed for course corrections. Freedman agreed. He noted that this was a very heavy payload. Launching it from French Guiana near the equator gave it an extra boost from the Earth’s rotation.

Wayne posted this link to stay on top of where is the JWST: https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html

For more information about upcoming events with the Humanist Society of Santa Barbara or to become a member, please go to https://www.sbhumanists.org/