The Wonder That Is Webb, Part 2

In Part 2 of this column, I talk a little more about the design of the James Webb Space Telescope (JWST) mirror, as well as the Canadian connection.

A telescope is all about collecting light. The more light you can collect, the fainter the object you can detect, which means the more distant the object. The amount of light collected also affects the resolution, or detail seen. So, the larger the telescope, the more light you can collect. The more light you can collect, the fainter the object and the more detail you can see.

On Earth, many telescopes use glass lenses to collect light. The bigger the lens, the more light you can collect. But using a large glass lens can be problematic. Glass is heavy, and the lens has to be ground to perfection to refract the light to the eyepiece (a much smaller lens) so you can see the object well. Sending glass lenses into space doesn’t work because a large glass lens is just too heavy. Heavy = more fuel. Fuel = $.

Most telescopes today use mirrors to reflect the light to the eyepiece (which is still a lens). The material used to make and coat mirrors is light, so telescope mirrors are easier to send into space, although a great deal of precision is still required to make the mirror surface reflect light perfectly.

As mentioned, we want a telescope mirror to be as large as possible to collect more light. The JWST mirror is made up of 18 hexagon mirrors positioned to approximate a circle as much as possible. Each hexagon is covered with an incredibly thin layer of gold, about one ten-thousandth the thickness of a human hair. The reason for the gold plating is because gold, being highly reflective, reflects infrared light well (the JWST collects infrared light).

The total amount of gold spread over the 18 hexagonal mirrors is about the same amount of gold that it takes to make five men’s wedding rings. Credit: NASA

But why hexagons? Why not just a round mirror, like the one that’s in the Hubble Space Telescope? The JWST mirror overall is 6.5 metres across, but the diameter of the rocket that carried the telescope into space is about 5.4 metres. So, to be able to build a large mirror to collect as much light as possible, the mirror has to be collapsible to fit in the rocket. The hexagon design allows for this.

The telescope is the size of a two-storey building, and the Sun shield is the size of a tennis court. So everything had to be folded up to fit inside the Ariane 5 rocket, which is only 5.4 metres in diameter. Credit: ArianeSpace.com

The three images of a galaxy called M74 shown below illustrate how we can learn different things about an object when using different wavelengths of light. The image of M74 on the left was taken by the Hubble Space Telescope using visible light. The image of the same galaxy on the right was taken by the JWST using infrared light. The image of M74 in the middle is a combination of the Hubble and JWST images.

In the Hubble image (left), the bright pink spots are star-forming regions. In the JWST image (right), we can see more structure in the spirals. The blue and pink are star-forming regions. In the combination of the other two images (middle), we can see even more structure in the spirals. The spirals seem to resemble snakes. The reddish areas are hot dust. All three images show hot young stars at the galaxy’s centre. Credit: ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST Team; acknowledgement: J. Schmidt

And what did Canada contribute? Canadian scientists and engineers built two important components of the JWST: the Fine Guidance Sensor and the Near-Infrared Imager and Slitless Spectrograph. The Fine Guidance Sensor helps the telescope figure out where it is pointing, locate the targets to observe and track them, and stay fixed on the targets. The Spectrograph helps identify the composition of the atmospheres of different solar system planets as well as exoplanets.

In return for these instruments, Canadian scientists will have guaranteed telescope time to have the JWST study exoplanets, galaxies, and more!

Discovering Exoplanets Using Starshade

Exoplanets are planets not in our solar system. Most exoplanets orbit other stars, but there are rogue planets out there, planets that don’t orbit a specific star but do orbit the centre of our galaxy. At the time of writing, over 5,000 exoplanets have been discovered, and astronomers expect that number to keep increasing.

There are different ways to discover exoplanets. One way is to measure the drop in a star’s intensity as a large planet passes in front of the star. This is called the transit method. Another way is to take a photo of a star thought to have its own solar system, but that isn’t always revealing. Stars are so bright that any planets in orbit around them get lost in the star’s glare.

Canadian planetary scientist Dr. Sara Seager is working with NASA on another way to find and study exoplanets. Dr. Seager’s particular goal is to find Earth-like exoplanets and, hopefully, some signs of microbial life.

Dr. Seager was born in Toronto, Ontario. She completed her B.Sc. at the University of Toronto and her Ph.D. at Harvard. She is currently on staff with the Massachusetts Institute of Technology as a Professor of Physics, Professor of Planetary Science, and a Professor of Aeronautics and Astronautics. Dr. Seager is also the current Honorary President of the Royal Astronomical Society of Canada.

 

Dr. Sara Seager. Credit NASA Exoplanet Exploration

The technology that Dr. Seager is involved with is called Starshade. Starshade is just that, a shade to cover a star. A shade attached to a telescope will be launched into space and programmed to image a star with known or potential exoplanets. The shade detaches itself from the telescope. Then the shade unfolds, much like a flower unfolds, to a width of about 50 metres. Then Starshade positions itself in a line with the telescope and the target star. The distance between Starshade and the telescope will be up to 50,000 kilometres.

With the brightness blocked, the exoplanets come into view. Instruments on the telescope will study the atmospheres of the exoplanets, yielding information such as the gases present. The types of gases will tell us whether life could be present.

The system is simple, although all technology has its benefits and challenges. For example, one benefit is, because so much of the starlight is blocked, the telescope doesn’t need an elaborate optics system. One challenge is dealing with the diffraction of starlight around Starshade (diffraction is the bending of light around an edge). Too much diffraction means the shadow made by Starshade may not be dark enough, which means it might be more difficult to see the exoplanets.

The program, called New Worlds, is still in its research and funding stage, so a launch date is not available yet.

Once Starshade positions itself between a star and Starshade’s telescope, any exoplanets pop into view. This artist’s conception of Starshade is not to scale. Credit: NASA and Northrop Grumman

This video from JPL shows how it will work.

 

Space Weather

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The term “space weather” will be new to some, but it’s becoming more and more important to be aware of. Space weather refers to the effect of solar emissions on our satellites and astronauts in space, as well as our electronics and electrical systems on Earth. By solar emissions we mean the solar wind, solar flares, and bigger events, called coronal mass ejections (CMEs).

Huge solar flares send charged particles toward Earth. Our magnetic field (the purple areas) and out atmosphere help protect us. Credit: NASA

If Earth is in the line of fire during a solar flare or CME, we are fairly well protected with our magnetic field and our atmosphere. But often the charged particles in the solar wind and emissions get through and we get auroras, or northern lights, for example. If the solar outbursts, or geomagnetic storms, are really large, then more charged particles get through, and they interfere with our electronics and electrical systems on Earth. One extreme example is the Carrington Event.

On September 2, 1859, a British astronomer named Richard Carrington was observing sunspots when he happened to observe a white solar flare on the Sun, which produced a huge CME. At the time, the science of space weather did not exist. Within hours, amazingly bright auroras appeared as far south as the tropics, which is not normal. In one report, the aurora was so bright that it woke up gold miners in the Rocky Mountains at 1:00 a.m.! They thought it was morning!

The geomagnetic storm was so strong that it caused electrical fires and knocked out several telegraph systems that took weeks to fix. Imagine what such a storm would do to our electronics and electrical systems today, being so much more extensive than in 1859. Although the electronics in satellites are made to withstand solar radiation, a major event could wipe out communications, Internet, and GPS services—a real disaster!

This graphic by the European Space Agency shows how excessive solar emissions can harm our astronauts, satellites, and electrical systems. Credit: ESA/Science Office, CC BY-SA 3.0 IGO

In a more recent example, on February 3, 2022, SpaceX launched 49 Starlink satellites. These satellites start off in a low-Earth orbit, about 200 kilometres above Earth’s surface. Eventually, they reach their operating altitude of about 550 kilometres. (Other satellites are in higher orbits: the International Space Station is around 400 kilometres above Earth’s surface, and our GPS satellites are around 20,000 kilometres above Earth’s surface.)

The next day, on February 4, there was a geomagnetic storm. Another effect of geomagnetic storms is that they warm up the atmosphere. When the atmosphere warms up, the density increases. When the density increases, atmospheric drag increases; in other words, more drag means that anything in the atmosphere starts to slow down faster than normal. While the atmosphere is pretty thin at 200 kilometres above Earth’s surface, it’s thick enough to affect the Starlink satellites. And it did. The drag proved to be too much. Most of the satellites couldn’t recover from the difference in drag, and maybe 40 of them will re-enter the atmosphere (if they haven’t already) and burn up. But at least that means there won’t be any space debris or danger to lives on Earth of falling satellite parts.

Space weather can also hurt any astronauts in space. During the Apollo Moon missions from 1969 to 1972, Canadian astronomers at the Algonquin Radio Observatory in Algonquin Park monitored the Sun, looking for any storms that could harm the astronauts. Had there been any, the astronauts could have been seriously harmed by the radiation, since the Moon has no atmosphere to protect them, and Earth’s magnetic field won’t help because the Moon is not within it. If needed, the Apollo astronauts would have left the lunar surface and sought protection in the Command Module in lunar orbit, which had thick walls to provide some protection from the radiation.

The Lucy Trojan Asteroid Mission

NASA’s Lucy mission is unique in that it’s the first to study a certain type of asteroid, called Trojans. Trojan asteroids share Jupiter’s orbit around the Sun. These asteroids may have formed farther out in the solar system than other asteroids we have studied. Ultimately, they have been caught by Jupiter’s gravity. They likely have different blends of the solar system’s starting materials than other asteroids we’ve previously visited. Consequently, Trojan asteroids have been called “fossils of planet formation” because scientists think they hold clues to understanding the formation of the solar system.

Launched on October 16, 2021, Lucy (the spacecraft) will visit seven of Jupiter’s Trojan asteroids between 2027 and 2033 (and one asteroid in the asteroid belt). These Trojan asteroids are situated at gravitationally stable points ahead of and behind Jupiter (Lagrangian points). There are two groups of Trojan asteroids. One group orbits the Sun in Jupiter’s orbit, preceding the planet. The other group trails Jupiter in its orbit. As more and more of these asteroids were discovered in the early 1900s, they were named after participants in the Trojan War as told in Homer’s epic work the Iliad. Asteroids orbiting ahead of Jupiter are named after Greek warriors, and the asteroids trailing Jupiter are named after Trojan warriors.

An artist’s impression of Lucy and two asteroids. Credit: NASA’s Goddard Space Flight Center/Conceptual Image Lab/Adriana Gutierrez

Lucy will visit seven Trojan asteroids and one asteroid in the asteroid belt. The mission relies on gravity assists to do this. The trailing Trojans are at L5, and the Trojans ahead of Jupiter are at L4. Image credit: NASA

You may be wondering if “Lucy” is a typical NASA acronym. It isn’t. The mission is named after the fossilized skeleton that helped scientists learn where humans fit into the evolutionary chain of life. The skeleton was discovered in Ethiopia in 1974, and she was named Lucy. Scientists hope that the Lucy asteroid mission will revolutionize our knowledge of planetary origins and the formation of the solar system.

Lucy will fly by Earth twice using gravity assists to speed up and head to Jupiter. These gravity assists will also be used to direct Lucy toward its targets. (See Gravity Assists below.)

Notice how Lucy speeds up as it goes around Earth. That’s the gravity assist. The first gravity assist will happen on October 16, 2022. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

Lucy will first make one huge loop out to Jupiter to visit some of the preceding Trojans. Then this looping path will take it back to Earth for another gravity assist, which will take it out to the trailing Trojans.

Lucy will continue cycling between the two groups of asteroids every six years. Lucy will not orbit these asteroids but will fly by them.

Note to Parents and Educators

There are some activities available at http://lucy.swri.edu/Graphics.html#Activities, such as colouring activities and a Lucy Paper Snowflake download.

Gravity Assists

A gravity assist uses the gravity of a planet (or the Sun) to slow a spacecraft down or speed it up. For instance, if a spacecraft is heading toward the Sun, the Sun’s gravity just starts pulling it in, and the spacecraft goes faster and faster. A gravity assist from Earth, Venus, or Mercury can be used to slow it down—the gravity assist acts as a brake, slowing the spacecraft down. Going the other way, say, to Jupiter, the spacecraft can use Earth’s gravity to increase its speed. With the gravity assist, there is a change in momentum, which changes the energy of the spacecraft. The gravity assist technique is the result of over 50 years of development of spacecraft navigation techniques. This technique is used to save fuel, which matters when designing an efficient spacecraft.