On the surface of any body in space (such as a planet or star), there is a certain
minimum speed that must be given to an object, which when directed
vertically upwards will allow the object to escape the gravitational
pull of that body, and for the Earth it has a value of 11 km/sec.
The sun, being much more massive than the earth, has a much larger
escape velocity of around 600 km/sec. Even so, activity on the
sun is often so violent that this velocity is exceeded and clouds of material
are ejected into interplanetary space.
The exact speed required for solar plasma to reach a planet in the
solar system depends on the distance of the planet from the sun, and
the height in the atmosphere from which the ejection takes place. This
is given by the formula:
v = sqrt { 2 G M ( 1/r1 - 1/r2 ) }
where v is in units of meters per second; M is the mass of the sun (1.991x10e30 Kg)
and G is the Universal Gravitation constant (6.67x10e(-11) in these units).
Escape velocities from various heights are given in the table
below. Heights are given in terms of the radius of the sun (denoted
Rs).
When observing mass ejections from the sun, there is a very simple
rule - escape velocity has been achieved if the material moves 0.1 solar
radius (70,000 km) in less than 2 minutes.
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