Curious Kids: is the sky blue on other planets?



Unlike Earth’s atmosphere, Jupiter’s ‘sky’ hosts magnificent shades of orange, white, brown and blue.
NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt, CC BY-SA

Jake Clark, University of Southern Queensland


Is the sky blue on other planets, like on Earth? What is an atmosphere, and do other planets have one? – Charlie, age 10



G’day Charlie, and thank you so much for your incredibly curious question.

Before I get too excited talking about the atmospheres of other planets, first we have to talk about what an atmosphere actually is.

Earth’s atmosphere is split into different layers.
ESA

The atmosphere is normally the outermost layer of a planet. On rocky worlds like Earth it is usually the lightest and thinnest layer.

The thing that makes an atmosphere an atmosphere is what it’s made of. It’s not made up of big lumps of rocks or huge swirling oceans; it is made up of gases.

What’s in an atmosphere?

Atmospheres can contain a wide variety of gases. Most of Earth’s atmosphere is a gas called nitrogen that doesn’t really react with anything. There’s also a fair bit of oxygen, which is what we need to breathe. There are also two other important gases called argon and carbon dioxide, and tiny amounts of lots of other ones.

The mix of gases is what gives a planet’s atmosphere its colour.




Read more:
Curious Kids: Why is the sky blue and where does it start?


Earth’s atmosphere is made up of gases that tend to bounce blue light in all directions (known as “scattering”) but let most other colours of light straight through. This scattered light is what gives Earth’s atmosphere its blue colour.

Do other planets have blue atmospheres? Some of them sure do!

The blue “haze” surrounding Earth in space is caused by the scattering of light from Earth’s atmosphere.

Other worlds

The atmospheres of the two ice giants in our solar system, Neptune and Uranus, are both beautiful shades of blue.

However, these atmospheres are a different blue than ours. It’s caused by the huge amounts of a gas called methane swirling around.

(Side note: methane is also the main component of farts. That’s right, there’s a layer of farts on Uranus.)

The atmosphere of Uranus (left) is slightly greener than Neptune’s (right).
NASA / JPL-Caltech / Björn Jónsson

Jupiter and Saturn, however, have completely different-coloured atmospheres.

Ice crystals made of a chemical called ammonia in Saturn’s upper atmosphere make it a pale shade of yellow.

Uranus’ atmosphere also contains some ammonia, which makes the planet a slightly greener shade than the deep blue we see on Neptune.

Jupiter’s atmosphere has distinctive brown and orange bands, thanks to gases that may contain the elements phosphorus and sulfur, and possibly even more complicated chemicals called hydrocarbons.**

The Juno spacecraft flying past Jupiter in 2017.

In some extreme cases, the entire planet might just be a huge atmosphere with no rocky surface at all. Astronomers and planetary scientists like myself are still trying to work out whether Jupiter and Saturn have rocky surfaces, deep down in their atmosphere, or whether they’re both simply huge balls of gas.

The Cassini spacecraft took this cracking image of Saturn back in 2010.
NASA/JPL-Caltech/Space Science Institute

However, there are some planets that have no atmosphere at all! The Sun’s closest and smallest neighbour, Mercury, is one example. Its surface is exposed to the vastness of space.

Beyond our solar system

So far I’ve been talking about the atmospheres of planets in our Solar system. But what about planets in other planetary systems, orbiting other stars?

Well, astronomers have been detecting the atmospheres of these planets (which we call “exoplanets”) for the past 20 years! It wasn’t until last year, however, that astronomers managed to detect the atmosphere of a rocky exoplanet. The planet is called LHS 3844b and it’s so far away that the light takes almost 50 years to reach us!

LHS 3844b weighs twice as much as Earth, and we astronomers thought it would have a pretty thick atmosphere. But, to our surprise, it has little to no atmosphere at all! So it might be more like Mercury than Earth.

Animation showing an artist’s impression on what LHS 3844b’s surface may look like.

We still have a lot to learn about far-off planets and discovering one with an Earth-like atmosphere that’s ripe for life is still many years away.

Maybe, Charlie, you could be the first astronomer to detect an Earth-like atmosphere on another world!The Conversation

Jake Clark, PhD Candidate, University of Southern Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.

All five bright planets come together in the morning sky


Tanya Hill, Museum Victoria

For the first time in more than 10 years, it will be possible to see all five bright planets together in the sky. Around an hour or so before sunrise, Mercury, Venus, Mars, Jupiter and Saturn, the five planets that have been observed since ancient times, will appear in a line that stretches from high in the north to low in the east.

The planets are visible from right across Australia in the dawn sky. You can start to look for the lineup from Wednesday, January 20 and it can be seen right through until the end of February.

Venus, Mars, Jupiter and Saturn have been in the morning sky since the beginning of the year. Jupiter is bright in the north, next comes reddish Mars, followed by pale Saturn and lastly brilliant Venus, which shines above the eastern horizon. It is the appearance of Mercury that makes the family complete.

Mercury has just transitioned from an evening object to a morning object. At first it will appear quite low to the eastern horizon and of all the planets it is also the faintest, so it will be hard to see to begin with. However, Mercury will continue to rise higher each morning and by early February it will sit just below bright Venus.

Dates with the moon

If you need something a little more to get you leaping out of bed before sunrise, then here are the dates to mark in your calendar. From the end of January, the moon will travel by each planet and can be used as an easy guide for your planet-spotting.

On January 28, the moon will be right next to Jupiter. Come February 1, the moon (in its Last Quarter phase) will be alongside Mars, then on the following morning it’ll sit just below the red planet. On the morning of February 4, the crescent moon will be near Saturn. Then on February 6, the moon will be alongside Venus and on February 7, a thin sliver of moon will sit below Mercury.

From January 28 through to February 7, the waning moon will travel through the line up of planets, passing each one in turn.
Museum Victoria/Stellarium

In line with the sun

The line formed by the planets in the sky closely follows the ecliptic, the apparent path of the sun against the background stars. This path marks the plane of our solar system, visual proof that the planets, including Earth, all orbit the sun on roughly the same plane.

The ecliptic is bordered by the constellations of the zodiac and one of the most recognisable zodiac constellations is Scorpius. If you’re awake before the first rays of the sun begin to drown out the stars, then look for the curved outline of the scorpion between Mars and Saturn. In fact, sitting just above Saturn is the red supergiant star Antares, which marks the heart of the scorpion and its reddish colour makes it the perfect rival for Mars.

Rare oddity

It’s been a long time since the orbits of all five planets have brought them together to the same patch of sky. To make the best of the viewing opportunity try and get to a clear open space where you can see from the north all the way across to the eastern horizon.

Position of the planets in their orbits around the sun as of February 2016.
from http://www.theplanetstoday.com

As early February comes around, I also highly recommend checking out the flight path of the International Space Station via websites such as Heavens Above or NASA’s Spot the Station.

The Station will be flying morning passes over Australia during that time and current predictions for each capital city have it travelling right through or near the line of planets, for example: Darwin (February 3), Brisbane (February 5), Perth (February 6), Sydney (February 7), Canberra (February 7), Adelaide (February 8), Melbourne (February 9) and Hobart (February 11). The predictions can change slightly, so best to check the websites closer to the date and be sure to enter your precise location to obtain the most accurate timing for the pass.

Finally, there’s still more to come. This August the five planets will be together again, visible in the evening sky, so stay tuned for more planet watching in 2016.

The Conversation

Tanya Hill, Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy), Museum Victoria

This article was originally published on The Conversation. Read the original article.