Astronomer Ken Tapping looks over some of the electronics at the Dominion Radio Astrophysical Observatory. Western News file photo

Star Gazing: Everything you need to know about Mercury

Ken Tapping is an astronomer with the NRC’s Dominion Radio Astrophysical Observatory, Penticton

Mercury is the closest known planet to the sun. It orbits only about 58 million kilometres from our star, compared with our 150 million.

Consequently, the intensity of the solar energy falling on Mercury’s surface is about seven times higher than the amount arriving here at the Earth.

Although it shines quite brightly in our skies, it is hard to spot. Many people have never seen it. The problem is that for us it can never be more than 23 degrees away from the sun. Never rising more than 1.5 hours before the sun or setting 1.5 hours after, we always see it against a bright sky. Mercury is one of the planets known from ancient times, well before the invention of the telescope.

At an average distance of 58 million km, Mercury orbits the sun much more quickly than we do, taking only 88 days to complete each trip. Its rapidly changing position in the sky, together with its elusiveness, led to the planet being named Mercury, after the Roman messenger of the gods.

Mercury is an interesting world. It is small, only 4,800 km in diameter, compared with our Earth’s 12,800 km. It is not much bigger than the moon, which has a diameter is 3,500 km. The moon is mainly a ball of basalt rock with a small iron core. However, Mercury is so massive it must be mostly a big ball of iron with a layer of rock on top. It could be that forming so close to the sun, blasted by heat and the intense solar wind from a young star, most of the light stuff was seared away, leaving iron. However, at this point we are still guessing.

Mercury is so close to the sun that the gravitational attraction on the side facing the sun is stronger than it is on the far side.

This pulls the planet a little out of shape. As the planet rotates it undergoes a gravitational ‘kneading,’ which is gradually slowing Mercury’s rotation, so that eventually the same side of Mercury will be facing the sun all the time, and its day will be as long as its year. That is the situation with our moon. The Earth’s gravity has stopped the moon’s rotation with respect to the Earth, so that it turns once for each orbit. This means we see only one side of it. This has not yet quite happened on Mercury, but with a day now lengthened to 59 of our days, 67 per cent of a Mercurian year, it is well on the way to becoming ‘locked.’

Mercury does not have much of an atmosphere, and its surface reflects only about 10 per cent of the solar energy hitting it. The lack of an atmosphere means heat can be rapidly absorbed by the surface, and then, during the long, 29.5-day nights, there is plenty of time to radiate that energy back to space and for the surface to cool off. The result is the biggest range of daily temperatures in the solar system. During the day, temperatures on the surface of Mercury can reach 430 C, and then dive to -173 C during the night.

Mercuryís axis is hardly tilted at all, so there are no seasons. This also means that near the poles there are craters where the sun never, ever shines. Those locations are the coldest places in the solar system, on the closest planet to the sun.

Despite being so interesting, Mercury has not attracted a lot of space missions. So far one spacecraft flew past and one other orbited the planet. One of the reasons for this is that being so close to the sun, Mercury is difficult to get to. Getting into a transfer orbit to Mercury requires a really large launcher or alternatively a complex set of fly-bys of other planets to achieve the required velocity. This approach reduces the size of the launcher but makes the trip take much longer — several years. There are plans for future orbiting missions, but currently there are no plans to put a spacecraft on the surface of the planet.

Saturn lies low in the southwest, getting lost in the twilight. Mars lies in the dawn glow, with brilliant Venus below and Jupiter below Venus. The moon will be new on Nov. 17.

Ken Tapping is an astronomer with the NRC’s Dominion Radio Astrophysical Observatory, Penticton.

Just Posted

The new event will allow kids to take part in Across the Lake Swim

A new free event just for kids will leave their hearts and… Continue reading

UPDATE: Kelowna stabbing victim tight lipped about incident

Police say 35-year-old North Okanagan man stabbed in Mission area Sunday won’t talk to investigators

Pumps run dry across the Central Okanagan

Kelowna, Peachland and West Kelowna all reporting gas shortages

UPDATE: Suspect sought in car theft

Stolen vehicle flees scene in Ashton Creek, found behind Polson Park in Vernon

Updated: Kelowna cops investigate armed robbery at city centre business

Robbery sparks late afternoon manhunt by armed police officers with guns drawn

Homeless people living on ‘Surrey Strip’ move into modular housing

BC Housing says 160 homeless people are being moved into temporary Whalley suites from June 19 to 21

BC Ferries posts strong earnings before rate cuts

Last year highest ever for vehicle traffic, most walk-ons in 20 years

More than 150 tremors hit Vancouver Island in last 24 hours

Seismologists monitor to see if pressure will be added to major fault

Snapchat used to make mass shooting threat in Kamloops

RCMP did not dub the threat a hoax, instead called it “unsubstantiated”

Amphitheatre planned for Kamloops area winery

Monte Creek Ranch Winery can finally proceed with amphitheatre plans

B.C. groups file response to government’s fight against solitary confinement

B.C. Supreme Court judge suspended ruling for one year to give government time to draft legislation

National sports organizations have to report allegations of abuse immediately

Sporting organizations will lose federal funding if abuse goes unreported, says Kirsty Duncan

BC conservation officers release badger from wolf trap

Badger recovering after being caught in trap near Williams Lake

B.C. Christian school mulls covenant, future of law school after court ruling

The university still wants to open a law school, but is looking at its options.

Most Read