Common Misconceptions

Highlighted from CREST quizzes

Table of Contents

The Solar System vs The Galaxy

Magnetic Field Generation

What is Tidal Locking?

What are Tidal Forces?

Titan

Interstellar Travel/Breakthrough Starshot

Habitable Zone vs GHZ

Exoplanet Detection Methods

Doppler Shift

Venus

Habitable Atmospheres

Water and Habitability

The Solar System and Beyond

The Solar System includes the planets, asteroids and comets that orbit the sun. There are multiple definitions of ‘the edge’ but the most common is where the sun’s gravitational field is stronger than that of other stars, called the heliosphere, which extends out to 90 Astronomical Units (1 AU= distance between earth and sun, Pluto orbits at an average of 40AU), but the oort cloud (the sphere of icy objects surrounding the solar system) is though to extend to at least 2000 AU. Beyond this, we reach our closest stars, which, along with the sun, are orbiting the centre of the galaxy. Our galaxy (AKA the Milky Way) consists of millions of stars, many of which have planets so are solar systems of their own! Our galaxy is just one of many that make up the universe. So- the planets (as well as asteroids and comets) orbit the sun (making up the solar system) and the sun orbits the centre of the milky way (our galaxy). 

So an exoplanet is any planet that does not orbit the sun- it could be orbiting another star or floating through space. 

The Sun is in the orion arm of the milky way, mid way between the edge and the core. 

Magnetic Fields

Electricity (including charge) and magnetism are intrinsically linked, as the fundamental force driving both is electromagnetism. Therefore a magnetic field can deflect the charged particles emitted by the sun that would otherwise be dangerous to life! A magnetic field is generated by the movement of a liquid metal core. 

What is tidal locking? 

When the planet/moon takes the same time to spin once on its axis as it takes to complete one orbit, so the same face always faces the body it orbits. Eg. the moon orbiting the earth, some exoplanets that are very close to their star (common in red dwarf systems). For planets tidally locked to their star, this could cause one side to be incredibly hot and the other cold, resulting in high speed winds.

What are tidal forces?

The forces that stretch a body (planet or moon) away from its centre of mass due to a difference in gravitational pull on either side. This is because the closer you are to a large object, the greater the force of gravity. Because this depends on the square of the distance, an object in a close orbit will experience much greater gravitational force on the near side than the far side, causing it to stretch. On earth, tidal forces from the moon cause the tides, but in objects that experience greater tidal forces it can stretch and squash the rock that makes up the planet, causing friction and heating it. This is the case for Enceladus and Europa, whose cores are heated by this friction, which then melts the bottom of the ice, creating a subsurface ocean! 

Titan

Bigger than Mercury, the second largest moon in the solar system but largest of Saturn. Only moon with a thick atmosphere. 

Interstellar Travel/Breakthrough Starshot

Breakthrough starshot consists of a few hundred nanocraft (very small and lightweight spacecraft) that will form a large flat ‘surface’ which will act as a lightsail. Lasers here on earth will be pointed at this, and the force of the photons hitting the spacecraft will cause it to accelerate. This will allow them to move at 20% the speed of light. If Proxima Centauri is 4 light years away, that means that light takes 4 years to get there. If Breakthrough Starshot is travelling at ⅕ of this, then it will take 20 years to reach the star. It will then beam back data in the form of light waves so will travel at the speed of light, reaching us 4 years after it was released from the spacecraft. Thus, after the launch of the spacecraft, it will take 20 years to reach P. Centauri and 4 years to beam back info, a total of 24 years. Proxima Centauri is the closest star to the sun, and is a red dwarf part of a multi-star system called Alpha centauri. 

Habitable Zones

The Habitable Zone is the area around a star where conditions may be right for life, generally governed by temperature. The Galactic Habitable Zone is the theorised areas of the galaxy where life could form around the stars within it. It is much more complicated, with distance from galactic centre (as too close in means too much radiation and too far out means too metal-poor), height above galactic plane and distance from dangerous objects like pulsars and black holes taken into account. 

Exoplanet Detection Methods

Kepler telescope (discovered most exoplanets) uses the transit method, which looks for dips in a star’s brightness when the planet passes in front and blocks out some of the light. It can tell us about the planets size and orbit, but not usually mass. VERY occasionally it is possible to figure out the mass when there are multiple planets in the system as their gravity will cause each others orbits to change slightly each time, but this is only possible when multiple planets are orbiting close to the star, so most of the time the transit method CAN NOT tell us the mass. To find the mass you have to use radial velocity, as the amount and speed that the star moves depends on the mass of the planet: larger planets = larger wobble.

Doppler Shift

When talking about doppler shift, make sure to talk about the change in wavelength not frequency, as the waves are still emitted at the same rate from the star, they are just distorted. 

Redshift = longer wavelength = moving away from observer

Blueshift = shorter wavelength = moving towards observer

Venus

Venus’ atmosphere (and the early atmospheres of Mars and Earth) is predominantly carbon dioxide, a greenhouse gas. This meant that when the sun aged and got hotter, more heat hit Venus and was trapped by the greenhouse gases. The rising temperature lead to Venus’ oceans boiling away, adding water vapour to the atmosphere. Water vapour is also a very potent greenhouse gas, adding to the warming. Usually, this would be regulated by the carbon cycle, which involves plate tectonics, but much of its tectonic activity stopped as  plates require water as a lubricant to move. 

Habitability- atmospheres

When asked about conditions for planet habitability, 43% of final quiz respondents said an atmosphere, but only 2 people suggested that it had to be suitable. For example, Venus’ atmosphere is what makes it pretty much uninhabitable, Mars’ is too thin, and the Gas Giants have *too much* atmosphere, to be habitable! This is because the atmosphere links to temperature, pressure and surface conditions!

Habitability and Water

Water is actually quite common in the galaxy, but it has to be liquid to be used by life. So a planet has to either: a) have a surface temperature suitable for liquid water, or b) have a subsurface lake where temp is suitable for water.

Thank you so much for taking part, I hope this has cleared up any confusion!