Samples from astroid will help scientists learn more about Earth

Collecting asteroid samples

On Sept. 25, a space capsule entered the atmosphere and parachuted to a soft landing in the Utah desert.

It brought with it a scientifically priceless cargo—samples of material from the surface of an asteroid. We hope this material from a distant astronomical body will provide important information about the formation of the Earth, and possibly how life got started.

On Sept. 8, 2016, an Atlas V rocket lifted off from Cape Canaveral, carrying a two-tonne spacecraft called OSIRIS-REX. This meticulously constructed acronym is short for "Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer".

Its destination was the asteroid Bennu. This object is comparatively small by asteroid standards, having a diameter of roughly 260 metres and weighing in at about 78 million tonnes. This asteroid was chosen because it passes close to the Earth, making it easier for us to get to compare it with its brethren orbiting the Sun between Mars and Jupiter.

In addition, there is a chance this asteroid could hit the Earth at some time in the future. So this was a chance to see what sort of body it is, in time to plan our countermeasures as and when the need arises.

The launch rocket did not have the power needed to put the spacecraft on a direct path to Bennu, so on Sept. 22, 2017, it did an Earth flyby to use our planet's gravity to change its course and speed. It arrived at Bennu in October 2020, and started to survey the asteroid's surface and to do a range of scientific studies.

On Oct. 20, 2017, it did a “touch and go” visit to Bennu's surface, grabbing a sample of the asteroid's material. Being so small, Bennu's gravity is so weak the spacecraft could be allowed to fall slowly to the surface, grab the sample and with a small blast from its thrusters, bounce back into space.

The spacecraft continued to survey the asteroid until April 7, 2021 and on May 10, it fired its engines to start its journey back to Earth. The precious sample of asteroid material was placed in a tightly sealed container and put into a capsule for dropping as the spacecraft flew past the Earth, en route to its next destination, Apophis, another potentially Earth-threatening asteroid, and therefore relatively easy to get to. With a diameter of about 350 metres, Apophis is a bit larger than Bennu.

We are very interested in asteroids because they are as close to being original samples of the construction material used to build the Solar System as we are likely to get.

Here on Earth, the weather, plate tectonics and our activities have modified, recycled and processed material to the point where there is nothing left of the primordial material that formed our world.

The rock samples brought back from the Moon by the Apollo astronauts and some robotic space vehicles are certainly less processed, but are they original? Our current idea is the Moon was formed when an object the size of Mars collided with the body that would become the Earth. As the wreckage coagulated into the Earth and Moon, it was almost certainly changed by the experience.

Apart from letting us know the ingredients from which the planets formed, and where our water came from and so on, the big question for us is does this raw material contain the chemical progenitors of life? If present, are they the basic chemical ingredients, or will they be more developed ones, like amino acids.

Canada contributed instrumentation for this mission, so we get some of the sample. A large portion of the material is going to be stored for future scientists to work on.

Another important result of this mission is hopefully that we can avoid getting a much bigger sample of this asteroid, delivered at high speed, free of charge, some time in the future.

•••

• Saturn rises in the southeast just after sunset, with Jupiter following about an hour later. Venus rises around 3 a.m. Mercury lies low in the dawn glow.

• The Moon will reach last quarter on the Oct.4.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.

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

Digital photography has revolutionized celestial renderings

Imaging the sky

Thanks to the steady flow of images from the Hubble Space Telescope and the James Webb Space Telescope onto the Internet and into the media, we are getting really used to stunning images of the cosmos.

Even amateurs, using backyard telescopes, can achieve images of a quality undreamed of even a decade or so ago. It is easy to forget that achieving these images is the end of a very hard road, over centuries.

When Galileo first pointed the telescope he made at the sky back in the early 17th century, he had to draw what he observed. Maybe surprisingly, this process of "imaging by hand" remained main stream in astronomy well into the 20th century.

Some astronomers do that today, spending hours at the telescope with a pencil and paper.

If photography became widely available in the 19th century, why did it not immediately take over? If you look at photographs of planets in astronomy books published as recently as the 1960s, you will see why. The photographs are usually blurry. There are two causes for this—the turbulence in our atmosphere and the long exposures needed to collect enough light to record the images.

Our turbulent and inhomogeneous atmosphere distorts the light waves from objects in space. This makes stars twinkle romantically. However, when we observe a planet, such as Mars, Jupiter or Saturn, we need to apply enough magnification for us to see surface details. Unfortunately this magnifies the atmospheric problems by more or less the same amount, giving us an image that shimmers or shakes, changing dramatically in fractions of a second.

Even with the light-collecting powers of telescopes, most cosmic objects are fairly faint, so exposures ranging from seconds to, in some cases, many hours are needed to collect enough light to build an image.

Unless the atmosphere is very steady, the result is a blurry image. That is because the camera recorded a superposition of many distorted images. Some astronomical objects appear quite large in the sky, they are just faint. For example the Andromeda Galaxy covers a patch of sky about twelve times the size of the Full Moon.

With little need of magnification, the atmosphere is not quite as much of a problem when imaging such objects. Atmospheric distortion can be partially avoided by putting our telescopes on the tops of mountains, above a good chunk of the atmosphere.

If we look through a telescope at a planet, we see that for occasional moments, the atmosphere steadies, the image stops jumping around and we see the details we seek. Then the dancing starts again. If we have a pencil and paper we can record the details we observed and wait patiently for the atmosphere to stabilize again, so we can grab some more details, gradually building up our image of the planet.

This requires great patience, but it does work, which is why this manual process of imaging has continued to be used, even in the age of photography. Then, in the last decade or so, digital cameras came to astronomy.

Imagine we are looking at an object where our telescope will need to collect light for an hour to build up a usable image. A continuous, long exposure will probably give us a useless blur. However, instead we can take lots of short exposures, over maybe several hours. Then afterwards we can select only the exposures that caught those rare moments of good seeing conditions. Then we combine them to build up the long exposure image we want. The result has been a revolution in astronomical imaging, for both professional and backyard astronomers. Just look in any astronomy magazine.

The other solution, available to those with the budget, is to avoid the whole atmosphere problem by putting our telescopes above that troublesome atmosphere.

•••

• Saturn rises around 9 p.m., Jupiter around 10 p.m., Venus around 4 a.m. and Mercury, low in the dawn glow, at 6 a.m. The Moon will be full on the Sept. 29.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.

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

Why are lunar craters round?

Shape of craters on moon

The next couple of weeks will be a good time to look at the Moon through binoculars or a telescope.

The best time to do this is not when the Moon is full. At that time, we are looking at it with the sunlight coming from behind us. We see no shadows, little detail and the glare can be awful. It is better to look at the Moon is when it is waxing or waning, so that part of the disc is illuminated, and we can see the terminator, the line between the lit and unlit parts of the disc.

If we were on the Moon, standing at the terminator, we would see the Sun rising or setting. Everything sticking up would be casting long shadows across the landscape. Along the terminator is the best place to look for detail.

The most common and eye-catching features on the lunar landscape are the craters—rings of mountains, often with a central peak. These are produced by impacts, rocky objects colliding with the Moon at extremely high speed—many kilometres per second. Some show radial streaks of material thrown out during the impact explosion.

Some areas are more or less saturated with craters, where they are crowded so densely that the impacts making new craters partially or totally obliterate existing ones. In other places there are dark, flat plains with relatively few craters. These areas are where huge lava flows buried or partially buried the existing craters, so the cratering process could start over.

In some places, lava filled the crater but left the rim. In other places only part of the rim was buried, leaving a C-shaped bay. There are also ring-shaped discolourations in the lava where craters were totally buried.

The Earth and Moon are about the same age, so our world must have been bombarded just as intensely in its youth. However, the continuous recycling of the surface by plate tectonic activities has erased most of them. What we see on the Moon, and also on the Earth, raises a very interesting question; why are craters generally circular?

Imagine a large stone ball, referred to as the impactor, hitting a rock face at a few hundred kilometres an hour, that is, at a subsonic speed. Basically, on impact the impactor tries to push the rock it is ploughing into out of the way. That is helped by shock waves moving ahead of it, which makes the rock crack and shatter.

Similarly, the impact sends shock waves back through the body of the impactor causing that too to shatter. If the impact is head-on, we get a round hole. If it is oblique, the mark is different, and the impactor might just bounce off. If we accelerate the impact to say 20 or 30 kilometres a second, or more, the story changes dramatically.

Because the impactor is now travelling far faster than sound, there are no shock waves launched ahead of the body when it hits. The material has no time to move out of the way, and there are no cracks moving back through the cannonball. The result is that instead of a mechanical impact, almost all the energy is converted into heat. Most of the impacting body and the material it has hit is heated to an extremely high temperature and vaporized. The result is a ball of very hot rock vapour under extreme pressure, which then explodes outwards in all directions, making a circular crater no matter at what angle the impactor came in.

Most of the impacts happened in the early years of the Solar System, while the planets and moons, including ours, were being built. There was a big asteroid impact 65 million years ago, which sealed the fate of the dinosaurs, there was a major impact in Arizona some 50,000 years ago and another in Tunguska in 1908, and they all left round craters or impact features. It might be that the age of frequent impacts is over, but they still happen.

•••

• The Sun crosses the equator, heading south, on Sept. 23, marking the autumn equinox and the official end of summer.

• Saturn rises around 8 p.m., Jupiter around 9 p.m., Venus around 4 a.m and Mercury, low in the dawn glow, at 6am. The Moon will reach first quarter on Sept. 22.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.

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

What happens when a universe comes to an end?

The end of a universe