Taking a closer look at the red dwarf star TRAPPIST-1

A star with seven planets

Photo: Pixabay

TRAPPIST-1 is a red dwarf star about 40.7 light-years away from Earth.

It is of particular interest because it has seven earth-like planets orbiting around it. The star was discovered using the Transiting Planets and Planetesimals Small Telescope (TRAPPIST), hence the rather strange name.

The planets were found by carefully monitoring the brightness of the star. If the planets have orbits taking them between the star and us, we will detect a tiny dimming of the star.

Amazingly, just from observing these transits, we can infer a lot about the planet in question. How long the planet takes to transit across the star's disc and the interval between these transits gives us a good idea of the planet's diameter and how long it takes to orbit its star.

That, in turn, gives us its distance from the star. Because we know how bright the star is, we can calculate how much energy is falling on the planet. From that, we can make a pretty good estimate of the planet's surface temperature.

In some cases, we can do a bit better than that. If the planet has an atmosphere, some of the starlight reaching us will have passed through it, picking up the signatures of the gases present. In that way, we can determine the main constituents of the planet's atmosphere. We have yet to find another planet—with the exception of ours—with a lot of oxygen in its atmosphere.

Red dwarf stars have both advantages and disadvantages for the existence of life on any planets they might have. The big plus is red dwarf stars have very long lives, during which their energy output does not change much.

Although TRAPPIST-1, a typical red dwarf star, has a mass of only about 10% the mass of the Sun and a surface temperature of less than 3,000 C, it is so miserly with radiating energy it will last much longer. It has been estimated this system is more than 7.5 billion years old and the star is still doing fine. The Sun is around 4.5 billion years old. When it reaches 7.5 billion years old, it will have become a red giant, fried its plants and then become a white dwarf star.

So planets of red dwarf stars have far more time for life to develop and evolve.

Because red dwarf stars are so dim, to be warm enough for liquid water to exist on their surfaces, any planets have to be orbiting much closer to the star and the range of distances where these conditions exist—the "Goldilocks Zone”—is much narrower. However, for Trappist-1, there are up to four planets orbiting in the Goldilocks Zone, with orbital periods of three weeks or less.

The big minus for being a planet orbiting closely around a red dwarf is that although these stars shine steadily for a long time, they are prone to super-sized versions of solar flares and planets orbiting close by are in point-blank range. On our world, solar flares disrupt our technology. A planet orbiting a red dwarf could have its atmosphere stripped away. That would be a major impediment to life getting started and then surviving.

Maybe that helps us get a clearer idea of what sort of stars are most likely to allow life to develop and evolve on their planets. Red dwarfs last a long time, but are dim, so planets have to orbit close to them, which makes them vulnerable to flares.

Really bright stars mean inhabitable planets would orbit at great distances, and be less vulnerable to flares but such stars have short lives. So we come back to sun-like stars, a compromise between brightness and long-term stability that seems to fit the bill, in at least one case.

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• The planetary parade is still fully in place, but Mercury, the closest planet to the Sun, and the most elusive, is now dropping back into the sunset glow. Saturn is still close by. Moving to the left, that is eastward, find brilliant Venus, then Jupiter, almost as bright; and Mars, conspicuously red. Start by looking in the western sky, as soon as the Sun has gone.

• The Moon will be full the tonight.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Accidental astronomical discoveries made by non-astronomers

Accidental discoveries

Photo: Pixabay

It might be surprising but two of the most important discoveries in radio astronomy were made by accident.

Maybe, just as surprisingly, they were made by engineers investigating radio communication issues, not "real" astronomers.

Back in the 1930s the new technology of radio offered, for the first time, the possibility of easy, worldwide communication. However, before the technology could be offered commercially, prospective companies needed to investigate its feasibility. Would interference disrupt the service? How often? What mitigation would be possible?

Bell was one of the companies planning to offer radio communication services, so it gave one of its engineers, Karl Jansky, the task of investigating any interference issues liable to cause significant disruptions. To do that, Jansky built an antenna and mounted it on the wheels from a discarded Model T Ford, so it could be rotated to determine the arrival direction of the interference.

Over the following weeks and months, Jansky catalogued interference from car ignition systems, electric motors and other devices, thunderstorms, power lines and other radio transmitters. When he identified them, he was left with something odd, a faint hissing in the headphones.

He rotated the antenna to determine the direction the hiss was coming from. Then he found something very odd. As time passed, the direction of maximum hiss moved slowly westward.

At that time, the sun was in the sky during the measurements and with his antenna not being very directional, he thought he might be getting radio emissions from the sun. That would have been a discovery anyway because to that point, no solar radio waves had been detected, or even expected to be there. However, a few months later that emission was turning up at night and Jansky concluded the hiss was actually radio emissions from the Milky Way.

The astronomical community did not receive the news well. Firstly, they thought all the electromagnetic emission coming from space would be due to the heat of the stars, coming to us directly or being re-radiated or reflected by cosmic clouds of dust.

If that were the case, the radio emissions would be very weak, and not worth bothering with, especially with the technology available at the time.

The second reason, which illustrates one of the less nice aspects of human nature, they saw Jansky as not an “approved” member of their community and suggested he should stick to playing with his radios.

Fortunately, Grote Reber, a radio amateur, heard about Jansky's discovery and built the first radio telescope, launching radio astronomy.

The accidental second discovery was made in the 1960s. At the time NASA was running Project Echo. It involved putting large balloons made of aluminium foil into space, with the intention of bounding radio communication signals off them.

For these tests, a horn antenna—looking rather like a huge ear trumpet—was set up for the purpose. Two engineers, Arno Penzias and Robert Wilson, were given the task of evaluating the test system. During the tests they found something odd. Just as Jansky did, they found a bit more signal than they expected. It came from all over the sky and was equivalent to a temperature of about 3.5 Kelvins.

In this case astronomical recognition was immediate because Robert Dicke and his team had been calculating whether we can detect any trace of the Big Bang today and estimated it would be a radio emission equivalent to a temperature of about 3.5 Kelvins.

However, before they had time to look for it, Dicke heard what Penzias and Wilson found and said to his colleagues "We've been scooped!".

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• The moon reached its first quarter on March 6.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Huge telescopes give a better picture of our solar system

Getting the big picture

Photo: DRAO

The CHIME Telescope, located at the Dominion Radio Astrophysical Observatory near Penticton.

Radio astronomy became an important branch of astronomy in the years following the Second World War.

In those days, the technology followed closely what was used in radar and communications. A typical radio telescope consisted of the biggest dish that available funds could provide, in order to collect as much of the weak cosmic radio emissions as possible. The dish focused the captured radio energy onto a small antenna, usually referred to as the “feed", which fed it to the radio receivers.

Systems like that were very useful for measuring the radio brightness and positions in the sky of cosmic radio sources, but were less useful for imaging. Basically, those radio telescopes were one-pixel cameras and making an image required scanning over the area of sky of interest, building up the image bit by bit.

That sort of imaging, or mapping, took a long time, and with intense competition by researchers for access to the larger, more sensitive radio telescopes, the large chunks of time needed for mapping projects were hard to get. If those projects got observing time at all, it was often on older, less-sensitive radio telescopes, for which the user-demand was less intense.

Fortunately, thanks to the dramatic advances in digital electronics over the last decade or two, the situation has changed dramatically. Now we can make radio telescopes that can take radio images of large areas of sky in a single operation and collect a wide-enough range of information to make it possible to collect data for multiple observing projects at the same time.

Of course, evolving from seeing the universe through a keyhole to having the whole picture was going to result in a lot of cosmic surprises.

The CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope at the Dominion Radio Astrophysical Observatory, near Penticton, was developed for studying the youth of the universe, when the primordial material from the Big Bang was organizing itself into the first stars and galaxies. To do that required an instrument that could observe large areas of sky simultaneously. That resulted in some entirely unexpected science surprises.

Some time earlier, the large, single-dish radio telescope at Parkes, Australia, just happened to be pointed in the right direction to detect a short, milliseconds duration intense pulse of radio emission from a source millions of light years away.

Such a short pulse means a small source, which in turn means a concentrated release of energy that is extremely large.

The CHIME radio telescope has now detected many thousands of those events. Such discoveries underline the importance of large, sensitive instruments that can observe large patches of sky with high sensitivity and has led to the current construction of a new, major instrument at Dominion Radio Astrophysical Observatory. It is called CHORD, the Canadian Hydrogen Observatory and Radio-transient Detector (the concoction of flashy acronyms is an important part of today's scientific research).

It will comprise a closely packed array of 512 sic-metre diameter dishes—rather like a giant insect's compound eye. There are other projects around the world, involving large numbers of relatively small antennas. The most ambitious is the Square Kilometre array, which will consist of thousands of antennas spread over South Africa and Australia. Canada is a partner in that project.

Although instruments like those are constructed with certain astronomical problems in mind, as we have found, their capabilities will open new avenues of research. Therefore, the data is recorded in as untouched a form as possible.

To ensure its accessibility to as large a research community as possible, and for it to be preserved for future use, it is stored in data centres, such as the Canadian Astronomy Data Centre.

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• The planetary line-up is nearly complete. Over the next few days Mercury will be sneaking up into the after-sunset glow, with Saturn close by. Moving to the left, (eastward) find brilliant Venus, then Jupiter, almost as bright and Mars, conspicuously red.

• The moon was be new yesterday (Feb. 27)

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Astronomers can take cosmic temperatures with specialized equipment

Taking cosmic temperatures

Photo: Wikipedia

The Dominion Radio Astrophysical Observatory, south of Penticton.

The Dominion Radio Astrophysical Observatory near Penticton sometimes gives tours to groups from local schools.

The tours often include demonstrations to help show what radio astronomy is all about. One of the devices that is occasionally rolled out for these tours is "The Cannon".

The equipment consists of a piece of copper tube around eight centimetres in diameter and about a metre long. On the end is a complex aluminium structure looking rather like a horn or the mouth of a blunderbuss. It is mounted, along with some electronics, on an equipment cart, so it intentionally looks like the sort of cannon pirates used to have lined up along the sides of their ships.

The device is completely harmless. It is a piece of prototype equipment used with the 46-metre in diameter dish in Algonquin Park, Ontario. The dish catches the weak radio emissions from cosmic radio sources and concentrates them at one point, the focus of the antenna, where they are collected by devices such as the one used in The Cannon.

Everything in the universe having a temperature higher than absolute zero (-273 C) emits radio waves. This is the idea behind the cannon demonstration. Volunteer students stand in front of this somewhat scary-looking device, so staff leading the tour can detect the radio emissions they are producing. It shows an important application of radio telescopes—we can use them to measure the temperatures of objects out in space, even if they are too cold to produce light or infrared radiation.

For example, we can measure the temperature on the moon without going there by just pointing a radio telescope at it. By making measurements at different wavelengths, we can measure temperatures at different depths below the soil level, and learn about the heat flows during the long lunar days and nights. That tells us about the composition and nature of lunar soils.

Using radio telescopes as cosmic thermometers has given us a few surprises. Maybe one of the biggest was when attempts were made in the 1950s and 1960s to measure the temperature of Venus.

Until then, because Venus is about the size of the Earth, permanently covered by cloud and closer to the sun, many scientists thought the planet's surface might be covered with a hot, steamy jungle, with lots of alien life forms waiting to be discovered.

Some, for no solid reason, hypothesized Venus could be like our planet as it was hundreds of millions of years ago. Then radio telescopes were turned on the planet. They revealed temperatures hot enough to melt lead and tin. However, the steamy jungle idea was so attractive, at first it was argued that those radio measurements were of the hot upper atmosphere, not the surface.

Finally, as the data accumulated, we had to accept Earth's sister planet is truly a hostile, hot, dry furnace of a world.

Radio telescopes have been used to measure the temperatures of other planets, and the temperatures of the dust and gas clouds between the stars. However, one of the most important discoveries was made by two engineers.

In 1964, Arno Penzias and Robert Wilson made accurate temperature measurements of radio emissions from the sky. They used an antenna shaped like a huge horn. However, they ran into a problem. No matter how carefully they did the measurements, the whole sky was three degrees Kelvin warmer than it should be.

Coincidentally, at the same time, Robert Dicke and other scientists finished a calculation that predicted if the universe started with a Big Bang, the echoes of the event should still be detectable and it would be a radio emission with a temperature of three degrees Kelvin.

Dicke and his co-workers had their answer. The universe started with the Big Bang. That three degree Kelvin emission is now known as the Cosmic Microwave Background.

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• The planetary line-up continues. Saturn lies low in the southwest sunset glow. Moving to the left (eastward) find brilliant Venus, then Jupiter, almost as bright and finally Mars, conspicuously red.

• The moon will reach last quarter on Feb. 20.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.