A hypothetical question – What if the Earth was twice as big? Meaning, what would happen if the Diameter of the Earth was doubled keeping its density same. The following six things will happen if such an event ever occured.
Earth is about 6,371 kms in radius. Let’s assume 6,400 kms for brevity. Twice of that would be 12,800 kms. Assuming the density to remain constant at an average of 5.5 g/cc, such an increase in radius would increase the planet’s mass and volume by 8.11 times and gravitational force by 2 times the present value.
This would mean, you’d feel twice as heavy. If you weigh 70 kilos today, you’d feel as heavy as 140 kilos! The acceleration due to gravity would now be 2g or 19.6 m/s/s which would mean objects will fall twice as fast towards the floor than earlier. It would also mean, objects falling from space would speed up twice as fast and burn up quicker in the upper atmosphere. It would take an object larger than 2 kms in diameter to impact the Earth’s surface in a single piece without disintegrating completely. That is still not enough to stop and burn the bolide that impacted the Earth causing the Dinosaur extinction event.
The increase of the size of Earth would still not make it bigger than the other existing larger planets and it’ll retain its 5th position in size of planets in the solar system. However, the enlarged Earth will be half as massive as Uranus and Neptune than it is now and Jupiter will be 39 times as massive still.
The Escape Velocity of Earth would now be 22.5 kms/s over the current 11.21 kms/s. Which would mean the rockets will have to be 2 times as powerful and would need to carry 8 times as much fuel as needed for same flight distances today. The orbital velocity required to maintain a circular orbit of the Earth at the altitude of the ISS would increase to 10.90 kms/s from 7.80 kms/s. This speed is almost the same needed to reach the Moon from Earth!
The atmosphere of the Earth; considering it has proportionately increased with the increase in size would become twice as heavy and more compressed due to increased gravitation. The surface pressures would increase to 202 kilopascals or 2 times the existing pressure. This is equivalent to the pressures at depths of 20 meters (66 feet) underwater. The average surface temperature would increase by an average of 10 degrees Celsius due higher capture of solar irradiation. The effective height of the Earth’s atmosphere is 65 kms. Above 65 kms, the static pressure drops to within single digits of Pascals. However, with the bigger earth, this height would decrease to 50 kms above sea level.
Due to increased downwards pull, evolution of life would tend to make organisms stubbier, stockier and shorter in height. In human beings, the spine would be compressed reducing the effective height. The diversity of crawling creatures would surpass the quadrupeds like we find today. Animals would look a lot different, shorter, stockier and a lot more muscular. All organisms would be built with different proportions than they are today. Bird as species would have either evolved lesser due to increased gravity and denser air, or they would have evolved highly diversified as large muscular birds like in the late cretaceous era due to higher gravity and denser atmosphere that could produce more lift.
There would no longer be tall trees. All vegetation would be shorter, more fern like. Tall trees would not have evolved at all. There would be a lot more grasslands and the equatorial and tropical forests would appear a lot denser due to shortened heights of most deciduous trees.
There are three possibilities here. Firstly, the moon would never have formed due to Earth’s increased gravity prohibiting the moon matter to collect in its orbit around the Earth after impacting it.
Secondly, the force of impact would have shattered the moon into smaller pieces that would lack momentum to escape Earth’s denser atmosphere and would form a much smaller and irregular asteroid like satellite instead of the spherical body as we see it today.
Third possibility is a ring system around the Earth as found around Neptune due to the tidal forces levied onto the moon by 8 times as massive Earth. The Moon would break up long before the impact with Earth and the ejecta would form a faint ring system around it.
The probability of the Third scenario is higher than the other two. Possibility of the Earth having more than one moon would be significantly high due to a deeper gravitational well. Higher gravity significantly increases the possibility of orbital capture of outside objects. We wouldn’t be surprised to have more than 3 moon like natural satellites for an Earth twice as large.
Rotation and Revolution Of Earth
The Rotational speed of the now larger Earth would decrease due conservation of Angular Momentum thereby increasing the length of the day from the current 23 hours 56 mins to 480 hours or 20 days! This directly translates to 10 days long days and 10 days long nights at the surface. This would create large spreads between diurnal and nocturnal temperatures. The daytime temperatures would soar to well above 100 degrees in equatorial regions due to prolonged exposures to solar irradiation. The night time similarly would be iced over to latitudes as low as 38 degrees north and south of the equator. The twilight on the planet would last for over 40 hours or just short of 2 days!
Due to increased mass, the relative distance between the Sun and Earth would decrease by 0.02 AU or 14,95,979 kms and the speed of revolution of Earth would increase from 29.9 km/s to 30.2 km/s thereby decreasing the length of a year by 4 days. This will eliminate the concept of the leap year that are caused due the loss of time to the difference between the sidereal day and the solar day.
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