Back To The Future

James Webb telescope, broadcasting 12th July

Courtesy of the European Space Agency (ESA)

The James Webb space telescope (JWST - named after a NASA admin bod) has been described as a time machine by many scientists. It will be hunting out life-supporting planets in our own galaxy as well as studying the universe shortly after the big bang 13.8 billion years ago.

What? How?

Telescopes

We have been looking up to the heavens with the naked eye for centuries. But it was only in 1610, when Galileo with the aid of a simple telescope, was able to publish an account of his observations of the Moon, Jupiter and the Milky Way called The Starry Messenger. It made him famous.

Being at school in the northwest of England, ensured at least one trip to Jodrell Bank, famous for the Lovell radio telescope - a 76 metre reflecting surface commissioned in 1957 and a significant landmark on the Cheshire Plain. It briefly featured in Hitchhiker's Guide to the Galaxy below a Vogon spaceship and in a Doctor Who series.

Another famous observatory is La Silla, on the fringes of the Atacama Desert, 600km north of Santiago de Chile at an altitude of 2400 metres. This remote location provides one of the darkest night skies on earth, far from any significant source of light pollution and home to the Very Large Telescope.

The obvious next exploration step, was to move beyond the earth’s atmosphere altogether, which is why the Hubble Space Telescope was launched back in 1990 and is still in use today, orbiting the earth. There have been others.

The JWST

The JWST is the latest space observatory. It launched in the nose cone of an Ariane 5 rocket to a bunch of nervous scientists on Christmas Day 2021. It’s a hugely ambitious, $10 billion project which has taken 20 years to build, suffering significant cost overruns and long delays.

It’s bigger and better than Hubble, which along with most ground-based telescopes, tend to focus on the visible part of the electromagnetic spectrum, which is best explained with this picture.

Courtesy of Encyclopedia Britannica

The JWST, which has a main mirror 6.5 metres in diameter, is only interested in the infrared part of the spectrum which means its cameras need to be well protected and kept cool from solar radiation with a 22 metre x 12 metre sunshield, which might otherwise result in dodgy signals.

Its permanent home took 30 days to reach, nearly a million miles from earth at a Lagrange point, L2. That’s a location in space, relatively near Earth that keeps it stable. The gravitational forces allow the telescope to stay in line with earth as it orbits the sun. It’s a popular spot and several other space telescopes have been positioned there previously.

How do you see the beginning of time?

Everything we see in the night sky takes time to travel to Earth. When we look at the moon, we’re seeing it a second ago, the sun about 8 minutes ago. That’s how long it takes for light to travel to and from those places to Earth. The longer it takes for light to reach us, the further back in time we’re looking.

Astronomers estimate the age of the universe at 13.8 billion years. If the JWST can see something 13.8 billion light years away, it is looking at something from the beginning of time.

Light buckets

It’s why telescopes are often called light buckets, because they’re designed to collect faint light. Bigger is better when it comes to telescopes because more light can be collected.

NASA

While the JWST might be the super new improved, it was Hubble that really opened up the possibility of out-of-this-world images of planets, firework-type displays of star clusters and galaxies.

NASA/ESA/M. Livio & Hubble 20th Anniversary Team

The two images provide a good example of the difference between visible light (left) and infrared (right), which identifies many more stars.

Exoplanets and life elsewhere

About 4,800 exoplanets have been detected around stars (like our sun), but not much is known about them. One of the next steps is to look for atmospheres around these planets, which is work that has to be done at the infrared wavelength.

The transit method is one way to study exoplanets. JWST will look for the dimming of light from a star as a planet orbits between the star and the telescope. Working with ground-based telescopes, it’s possible to measure the mass of these planets by measuring the stellar wobble - the gravitational pull exerted by a planet.

The telescope will also measure the intensity of light at different wavelengths as the planet passes in front of the star. This is called spectroscopy and the graphical presentation of these measurements are called spectra. Because different elements and molecules absorb light at specific energy levels, it’s possible to detect the signature of methane or water, if it’s present in one of these new planet’s atmosphere.

What’s happening now?

Since arriving, JWST has been undergoing lots of tests, calibrating its instruments in its new space environment and aligning its mirrors. Once the science and engineering teams are satisfied, the team has a list of targets, chosen by an international committee to show the new telescopes powerful capabilities, processing them into images for all to see. These first visuals are expected to be revealed on the 12th July here.

Then what?

Teams of scientists have already applied through a competitive process for time to use the telescope to advance their particular science projects. I expect scheduling has been carefully managed, to ensure the time available is used as efficiently as possible in this first cycle of observations. It means astronomers will now be able to observe the infrared Universe, analyse the data collected and publish their findings.

They are also likely to be expecting the unexpected. In 1990, when the Hubble Telescope launched, dark energy - a hypothetical energy form that exerts a negative, repulsive pressure, the opposite of gravity, was completely unknown. It’s now one of the hottest topics in astronomy.

The first images shown, which take several weeks to a month to process from the raw data, will highlight the science themes that led to the mission - early universe, evolution of galaxies, lifecycle of stars and other worlds.