ART HOBSON: A New Era in Astronomy

Humans have long been fascinated by the sky. Our first stories are about heroes buried among the stars. Ancient structures such as Stonehenge were built to mark the apparent movements of the sun. Galileo in 1609 pointed a first telescope at the rings of Saturn and the moons of Jupiter, triggering a cultural revolution that overturned superstitions and reoriented humanity towards an enlightened humanism based on experience.

A new era of astronomy, and perhaps scientific history, begins (hopefully) tomorrow, when the James Webb Space Telescope goes into Earth orbit. Webb has five times the light-gathering power of the 31-year-old Hubble Space Telescope. While Hubble primarily detected visible light, Webb will primarily detect non-visible infrared “light” with a slightly longer wavelength. This is advantageous because the universe has expanded over its 13.8 billion year history, stretching light waves into infrared waves.

To get a glimpse of the technical finesse of this breathtaking instrument, consider its primary mirror which reflects incoming infrared to a secondary mirror and then to a detector. It is made up of 18 hexagonal mirrors assembled in a honeycomb pattern – a perfect mirror covering 357 square feet. The mirrors are made of beryllium coated with a very thin layer of highly reflective gold which has been placed on the surface by “vacuum vapor deposition” in which small amounts of gold are vaporized and deposited on the surface of the mirror. beryllium. A thin layer of glass was then deposited on the gold layer to protect it from scratches. The total weight of gold, a heavy metal, was only 50 grams or 1.8 ounces – the weight of a golf ball!

After launch, project engineers will experience 30 days of terror as Webb deploys its solar power panels, communications antenna, huge sunshade and mirrors. It must then position itself in orbit around the Earth at a point of gravitational equilibrium called “L2”, located 1.5 million kilometers from Earth, too far away to be repaired by visiting astronauts. It must therefore work perfectly from the start. Unable to be refueled, it will have a limited lifespan. The limiting factor is the propellant that drives its repositioning thrusters, which will run out in 5 to 10 years.

Over the course of these years, Webb will bring back data to Earth covering everything from the days when the first stars began to shine, to the mysterious invisible dark matter that comprises 85% of the matter in the universe, to a deeper understanding of our own solar system, the conditions on other planets orbiting other stars, and whether those planets could provide habitat for life.

Webb is expected to spot evidence of the first stars formed directly from the simpler atoms, hydrogen and helium, created in the first minutes of the Big Bang. Some 200 million years later, as the universe expanded and cooled, hydrogen and helium gas came together by gravity to form stars. These early stars were perhaps 1,000 times more massive (heavier) than our sun, causing them to “burn” (ie merge their atomic nuclei together) quickly and furiously, which depleted their fuel. fusion in just a few million years. Hundreds of millions of years later, the first galaxies formed.

What about life in the universe? Astronomers discovered the first “exoplanets” around other stars in the 1990s. We have now found thousands of them and consider them to be the norm around other stars. Webb will learn to know them better, to study how they were born, to dissect their material and, above all, to study their atmospheres. The idea is to detect a planet as it orbits directly in front of (as seen from Webb) its star. Starlight passing through the planet’s atmosphere is altered by being partially absorbed. Webb receives this light and studies its “spectrum,” from which scientists can infer many chemicals in the exoplanet’s atmosphere.

Hubble and other telescopes have already detected water vapor, methane, and carbon monoxide in the atmospheres of exoplanets. Webb will detect these and many other elements, some (like water) essential to life as we know it and others (like methane) compatible with life. A knowledgeable scientist said that “Webb would open the door wide” to the chemistry of exoplanets. Webb will sniff the atmospheres of rocky planets similar to Earth, but might not be able to detect direct signs of life such as oxygen or chlorophyll. With the help of a shield that blocks the crushing glare of a star from an exoplanet, Webb will even be able to photograph some exoplanets.

Although Webb captures spectacular data on exoplanets, compelling evidence of life on other worlds will likely have to wait for an even larger space telescope.


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