The Sun has a powerful gravitational pull, so why are all the planets drifting away from our star?

The Sun, with its gravity, holds all the objects in the Solar System together as a single entity. This means that in this region of space, our star is the dominant object with the strongest gravitational pull, causing all the planets to orbit around it. At the same time, however, the planets are moving away from the Sun. Why is this happening? This is discussed by IFLScience.

Why Are the Planets in the Solar System Moving Away from the Sun?

One common question people have regarding the orbits of planets is why they are moving away from the Sun, given the strong gravity of our star that holds the entire Solar System together.

Calculations by scientists show that, for example, the Earth is moving away from the Sun at approximately 1.5 cm each year. The same applies to the other seven planets in the Solar System, although the distance by which their orbits change varies for each planet.

It is known that the Universe is constantly expanding, and it is doing so with a steady acceleration, driven by the mysterious force of dark energy. However, the Earth and the planets are not moving away from the Sun due to dark energy. The expansion of space occurs only in regions where different objects are not bound together by strong gravity.

Thus, the expansion of the Universe does not affect the distance between objects in the Solar System, as they are held together by the Sun's gravity. In contrast, distant galaxies are not bound by gravity, which is why they move away from each other as space expands.

The reason why the planets did not initially collide with the Sun lies in their lateral motion. For instance, the Earth moves around the Sun almost entirely sideways relative to our star at a speed of about 108,000 km/h. If this lateral motion were removed, the planet would move closer to the Sun. This motion was imparted to the planets when they formed in the protoplanetary disk, a cloud of gas and dust surrounding the young Sun more than 4.5 billion years ago.

Does this mean that the reason the planets are moving away from the Sun is that they are somehow accelerating? The answer is no. The reason lies in the fact that the Sun is very slowly converting mass into energy during nuclear fusion and losing mass through solar wind.

As the Sun converts hydrogen into helium in its core during nuclear fusion, the mass of our star decreases, emitting electromagnetic radiation. The loss of mass leads to a reduction in the star's gravitational force, causing the orbits of the planets to expand. Scientists estimate that the Sun loses about 10 to the power of minus 13 of its mass each year, which corresponds to an increase in the Earth's orbit of 1.5 cm annually.

Why Might Some Planets in the Solar System Collide with the Sun?

Scientists suggest that the Sun, at the end of its life, may engulf the inner planets of the Solar System, including Earth. Although this contradicts the notion that planets are moving away from the star, the reason for this potential outcome lies in how the Sun will evolve in the later stages of its life.

All stars similar to the Sun, and even those that are at most eight times its mass, end their lives in a similar manner. When the hydrogen in the star's core is depleted for sustaining nuclear fusion, it begins to contract under the influence of gravity. There is simply no energy from fusion to counteract gravity. The contraction of the star's core leads to an increase in temperature and pressure, resulting in the conversion of helium into carbon, releasing energy. Thus, the remaining hydrogen continues nuclear fusion, but in the star's outer layers, causing it to expand. In approximately 5 billion years, a red giant star will form in the place where the Sun once was. The expansion of the Sun will cause it to engulf Mercury and Venus, and possibly even Earth.