Dancing close to the sun

Almost all the solar information we have is either acquired from instruments located on Earth, or in near-Earth space.

This raises two issues.

  • We are too far away to see many of the fine details necessary to understand what the Sun is doing.
  • We infer conditions on the Sun through interpretation of light, radio waves and other solar emissions.

It would be useful to go to the Sun, to measure the solar environment directly, to check if our thinking is right, or to correct what we are getting wrong.

Two spacecraft have been sent to the Sun to meet these needs. One is the European Space Agency's Solar Orbiter; the other is NASA's Parker Solar Probe.

The Solar Orbiter's path around the Sun takes it within 43 million kilometres of the solar surface, giving us sharper and more detailed images than we have ever had. 

It will be exposed to about 12 times the level of heat and radiation we encounter on Earth.

The Parker Solar Probe passes much closer to the Sun, dipping down to within seven million kilometres, in order to sample solar material and magnetic fields directly.

It will be exposed to more than 40 times more heat and radiation than Solar Orbiter does.

In addition to the technical problems involved with building spacecraft to survive such missions, dropping spacecraft so close to the Sun requires very big launcher vehicles and some very clever gravitational manoeuvring.

We are very interested in the Sun for two reasons.

  • It is the only star close enough for easy observation, making it the reference case for our studies of other stars.
  • The Sun provides all our light and heat, making our world habitable, and its bad behaviour can degrade or destroy the technical infrastructure on which our modern lives depend.

For example, in November 1989, a solar flare and coronal-mass ejection caused a massive power outage in Quebec, along with other damage. The total impact was around $2 billion.

This is why nations around the world are investing in solar monitoring programmes, using instrumentation on the ground and in space.

We make two main sorts of measurements of the Sun. There are "sun as a star" measurements, where we monitor some aspect of the Sun as a whole — for example, counts of sunspots or measurements of the 10.7cm solar radio flux, which Canada has made since 1947.

These, continued over years, help us understand the behaviour of the Sun as a star, and to assess the impact of long-term solar behaviour on climate and other environmental factors here on Earth.

The other sort of measurements are conducted over shorter periods, but tell us things that help us check whether our understanding of solar processes is anything like correct.

The better our knowledge of how the Sun works the better we will comprehend what our long-term solar monitoring is telling us.

The environments the Solar Orbiter and the Parker Sun Probe are having to tolerate will mean they are not likely to provide long-term data.

However, they are already giving valuable information about what is happening on the small scales unobservable from the Earth, making it possible to check our understanding of the magnetic machine in the Sun. 

In addition, we are at last getting direct measurements of the environmental conditions in the solar atmosphere, as opposed to inferring them from observations made from Earth.

However, measurements made from the ground are vital in that we can make them consistently and for long periods of time; we just need to be sure we understand as much as possible what we are measuring.

  • Saturn and Jupiter lie low in the southern sky overnight
  • Mars rises around 11 p.m.
  • Venus, shining even brighter than Jupiter, rises around 3 a.m.
  • The Moon will be new on the 18th and will reach First Quarter on the 25th.

Living on Mars

At some point in the next decade or two, one of us is going to plant a space-suited foot on the surface of Mars and make that first footprint.

However, that first trip to Mars will not involve a couple of days in a spacecraft, a few hours on the surface grabbing rocks and taking pictures, before heading home.

Using current space technology, getting from Earth to Mars takes a few months. Then, when we get there, we cannot fill some bags with samples, take some pictures and head home, because we will have to wait until Earth and Mars are in the right relative positions for the return trip.

This means we will have to have a Mars base suitable for living in comfortably for a few months, in other words, not far short of a permanently manned base, or even a good practice run for the first colony.

Long ago, Mars was a warm, wet world with a thick atmosphere, just like our Earth. However, because Mars is a smaller world than Earth, its core solidified much faster and the planet's magnetic field decayed.

This let the solar wind hit the top of the atmosphere to start scouring it away. Mars' gravity is less than Earth's allowing the atmosphere to spread further upward, enhancing the rate at which it is still being lost to space.

The result is that today the Red Planet is a cold, almost airless desert. The air pressure is about 0.3% of the air pressure on the Earth's surface, so that even if it were pure oxygen, each breath would bring in nowhere near enough oxygen for us to survive.

However, there is very little oxygen in Mars' atmosphere. In addition, even through a warm, summer's day on the Martian equator might reach 20 degrees Celsius, at night the temperature will drop far below zero, and over most of Mars, it is well below zero all the time.

The result is that for us to survive on Mars, we will have to live in sealed habitats, under bubbles, as depicted in science fiction stories, or, more likely, in underground habitats, where the soil acts as insulation against the temperature variations and protection against radiation.

If we want to work outside we will need spacesuits, or ride in sealed, insulated vehicles. Living like this will be highly inconvenient for those living and working on the planet over years, or lifetimes.

We know that Mars was once very much like the Earth. Could we make it like that again? Could we terraform Mars?

Various methods are talked about, genetically modified plants that like the local environment and spit out oxygen, or numerous industrial scale machine complexes that do the same thing, or maybe a mixture of both.

For example, pump a lot of carbon dioxide into the atmosphere to increase the greenhouse effect and the temperature, which will then melt the ice, liberating water, and provide a starting point for getting vegetation going.

This would take in the carbon dioxide and release oxygen.

We would hope that the dense atmosphere would still have enough greenhouse effect to keep things warm.

However, the processes that turned Mars from warm and watery to cold and dry will still be active, and that atmosphere we would be working hard to produce would continue to flowing off into space. Our terraforming process would therefore be an ongoing fight with Mother Nature.

There is another very important issue: If we find there is still some form of life on Mars, even bacteria, making the planet right for us would make it hostile to them. Have we the moral right to do that?

When we find life "out there,” we should respect its right to exist, as we expect would be the case when alien visitors arrive at our world and start complaining about the surface conditions.

  • Jupiter is conspicuous in the south overnight.
  • Saturn is to its left.
  • Mars rises around 11 p.m.
  • Venus, shining even brighter than Jupiter, appears in the early hours.
  • The Moon will reach Last Quarter on the 11th, and be New on the 18th.

Planet still missing

In the 18th Century, Johann Bode and Johann Titius came up with a strange procedure for predicting where to look for planets.

It seems more like a numbers game than a scientific tool.

Make a little table with four columns. A spreadsheet program provides a nice way to do this.

  • In column 1, write the numbers 1 to 8.
  • In column 2, put zero at the top, then a 3 below it, and below that just keep doubling the number above:
    3, 6, 12, 24 etc.
  • In column 3, add 4 to the numbers in the second column: 4, 7, 10, 16, 28, etc.
  • Divide the numbers in the third column by 10, and put the results in the fourth column, which gives:
    0.4, 0.7, 1, 1.6, 2.8, 5.2, 10, 19.6.and 38.8.

In order to make the distances in the Solar System easy to comprehend, we define the average distance between the Earth and Sun as 1 astronomical unit (1 au).

Using this convention, the distances of the planets from the Sun are:

  • Mercury (0.4 au),
  • Venus (0.7 au)
  • Earth (1 au)
  • Mars (1.5 au)
  • Jupiter (5.2 au)
  • Saturn (9.8 au),
  • Uranus (19 au)
  • Neptune (30 au).

That strange series of numbers concocted by Bode and Titius are either exactly or close to the actual distances the planets lie from the Sun.

Uranus was discovered after Bode and Titius put together their number series, and was exactly at the predicted distance. This gave that list of numbers huge credibility.

Fascinatingly though, the numbers also suggested there should be a planet orbiting at 2.8 au, between the orbits of Mars and Jupiter, and there wasn't one. The search was on.

Finally, in 1801 Piazzi found something. Initially it was believed to be the missing planet, and it was named Ceres.

However, it turned out that this new discovery has a diameter of less than 1,000 kilometres, which is far smaller than the Moon, and definitely not big enough to qualify as a planet.

A year later another object turned up. Named Pallas, it was even smaller, with a diameter of a bit over 500 km.

By 1807, the count was up to four, with Vesta and Juno added to the list. Vesta is about the same size as Pallas, and Juno a bit more than half the size.

Instead of a planet, there were multiple small bodies sharing similar orbits between Mars and Jupiter. These new objects came to be called planetoids, or, less accurately, asteroids. The less accurate name is the one that stuck.

As telescopes got bigger, and cameras started to be attached to telescopes, the number of new discoveries rocketed. Astronomers carefully stabilized their telescopes over hours to collect enough light to image distant galaxies, and then found asteroids had made unsightly tracks across the images as they drifted past.

Because of this, asteroids soon became known as the "vermin of the skies.”

However, until recently, nobody knew why, instead of a planet between Mars and Jupiter, there is an enormous collection of rubble, ranging from dust and gravel to a body the size of Ceres.

Today, we have a possible explanation. The story starts back when the Solar System formed.

A great cloud of gas and dust collapsed into a rotating disc, and then as the disc got smaller, denser and rotated faster, the core formed the Sun, and in the surrounding disc, "diskettes" formed, each of which formed a planet, except for one.

The problem was that one of those diskettes had accumulated a large amount of material and formed the giant planet Jupiter. Then, the strong gravity of that planet interfered with the neighbouring diskette toward the Sun, preventing it forming a planet, and leaving it as a huge collection of smaller bodies.

We have an explanation for the missing planet, but we still have no good explanation for that series of numbers Bode and Titius put together.

  • Jupiter is conspicuous in the south overnight
  • Saturn is to its left.
  • Mars rises around midnight
  • Venus, shining even brighter than Jupiter, appears shortly before dawn.
  • The Moon will reach Last Quarter on the 11th.

The world that never was

Neptune was the first planet discovered by detecting and measuring deviations of known planets from the predicted orbits.

From these measurements astronomers calculated how big a body was causing it and where to look.

The sky is a very big place, especially when we are looking through telescopes that can see only a tiny bit at any one time. We need to know where exactly to look, and when.

After this method triumphed in finding Neptune, the search was on for other unknown planets. Almost immediately, the attention of astronomers was drawn to Mercury, the closest planet to the Sun. There was something funny about the planet's orbit.

All the planets have very slightly egg-shaped orbits, so there is one point where they are at their closest to the Sun (the perihelion) and at the other end of the orbit, where they are at their furthest (the aphelion).

Strangely, instead of the orientation staying fixed compared with the stars, it was slowly slipping, or precessing. Something had to be causing it, maybe an unknown planet.

Astronomers made measurements, calculated, and then concluded the perturbations to Mercury's orbit indicated there was a planet orbiting the Sun even closer than Mercury.

They were so sure that even before the planet had been found, it was given a name, Vulcan, after the Roman god of fire. Temperatures on the surface of Mercury are high enough to melt lead. Vulcan would be far hotter.

Mercury is a hard planet to observe. Since it orbits close to the Sun, most of the time it is lost in the Sun's glare. We only get to see it when it is at the eastern or western extremes of its orbit.

Then, it is at a large enough angle from the Sun for it to rise in a reasonably dark sky before sunrise, or to set long enough after the Sun for most of the glare to have gone.

Vulcan was expected to be far harder to find, so even when astronomers searched the predicted positions and failed to find it, they were convinced it was probably there, somewhere, and continued searching.

There was the odd report of someone actually finding it, but the observations could not be repeated and were not consistent. Finally, in the early years of the 20th Century, someone came up with a new branch of physics that offered a completely different explanation for the problems with Mercury's orbit.

The scientist was Albert Einstein and the explanation for the orbit problems was the distortion of space-time due to being close to the large mass of the Sun.

All objects bend space-time, similar to the distortion of a trampoline when we drop a bowling ball or other heavy object on it. Because Mercury's orbit takes it nearer to and further from the Sun, it moves between its perihelion, where space-time is more distorted, out to its aphelion, where it the distortion is less.

It is this that causes the orbit to precess, and Vulcan became the "planet that never was,” or maybe not. What, if anything did those reports of sightings of Vulcan mean?

There are two satellites sharing Earth's orbit around the Sun, one leading and one trailing. The pair, called STEREO is being used to make high quality, 3D images of the Sun and coronal mass ejections, and to provide a more complete view of our star.

A search through the STEREO database has come up with nothing, which means there is nothing there bigger than about six-kilometre diameter, other than asteroids with orbits taking them close to the Sun and then far out into the Solar System.

The only planet Vulcan we know of is the fictional Mr. Spock's home world. That planet is said to orbit the star 40 Eridani A, which lies 16 light years away.

Astronomers recently discovered a planet orbiting that star. Guess what they called it?

  • Jupiter and Saturn rise around 9 p.m.
  • Mars rises around midnight and Venus at 3 a.m.
  • Mercury might be discernible low in the dawn glow, rising about 4 a.m.
  • The Moon will be full on the third.

More Skywatching articles

About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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