The Christmas asteroid challenge proposed by the European Space Agency (ESA) started two days ago when asteroid 2015 RN35 arrived within 686,000 km of our planet. The asteroid has a magnitude of around 14, it is between 60-140 m in size and it takes 654 days to orbit our sun. ESA encourages all who partake to share their observation on social media using the hashtag #ESAChristmasAsteroid. What are asteroids though? Here are 10 asteroid facts to help you identify one.
#1 The cradle
Most asteroids orbit in the asteroid belt, between the orbits of Mars and Jupiter.
#2 Jupiter scattered it all
Asteroids are not fragments of a disintegrated planet, but fragments of planetary bodies that could not accrete to form a planet due to Jupiter’s strong gravitational force.
#3 Near Earth
Near Earth Asteroids (NEAs) have orbits bringing these celestial bodies near or across Earth’s orbit. To date, there are over 30,000 NEAs that we know of.
#4 Hazardous Asteroids
The type of NEAs that could potentially collide with Earth in the future, are called Potentially Hazardous Asteroids (PHAs).
#5 Never ending story
Although the lifetime of NEAs is short compared to our Solar System due to their constant collisions with terrestrial (Earth-like) planets, there are still numerous left, implying that the supply of NEAs is replenished. Scientists found that this happens by the inner asteroid belt’s orbital evolution, delivering NEAs into the inner Solar System.
#6 Size matters
When talking about impacts it is important to know the size, velocity, composition, strength and porosity of the asteroid and the gravity and composition of the target body. However, it is safe to say that for an asteroid that could cause a mass extinction event on Earth and even change the climate, it would have to be at least 10 km across. Just for comparison, the largest main belt asteroid is Ceres, with a diameter of 915 km.
#7 Listen to the radio
Although encountering asteroids with a spacecraft is a great way of gathering information about these celestial objects, it is not the only way. Radio astronomy techniques can also be used to image an asteroid and thus get detailed information of it.
#8 It takes two
Asteroids can form binary systems, traveling through space together like Didymos and Dimorphos. The latter was the target of NASA’s DART (Double Asteroid Redirection Test) mission earlier this year. Albeit the 160-meter asteroid not posing a threat to Earth, NASA wanted to test its kinetic impactor that was designed to change the orbital speed of the celestial body.
Asteroids that produce craters on Earth have an average encounter velocity of 19 km/s at the top of our planet’s atmosphere.
#10 Shedding light on shapes
Our sun illuminates the asteroids as they make their way through the Solar System. As the asteroids rotate and light is reflected from their surface, they produce lightcurves. These vary depending on the shape of the object: a changing brightness means a non-spherical object, while a spherical object displays very little variation in its lightcurve. Similarly, the period of these curves can shed light on how elongated the asteroid is.
Featured image: Asteroid moonlet Dimorphos as seen by the DART spacecraft 11 seconds before impact. Credit: NASA/Johns Hopkins APL