Why there is no moon in mercury and venus ?
Most likely because they are too close to the Sun. Any moon with too great a distance from these planets would be in an unstable orbit and be captured by the Sun. If they were too close to these planets they would be destroyed by tidal gravitational forces. The zones where moons around these planets could be stable over billions of years is probably so narrow that no body was ever captured into orbit, or created in situ when the planets were first being accreted.
Moons or natural satellites are either created during the creation of the planet/solar system, or are captured.
Mercury doesn't have a gravitational pull powerful enough to hold anything else in orbit around itself. That's why it doesn't even have an atmosphere. And proximity to the Sun ensures that any object coming within Mercury's vicinity is sucked into the Sun directly. So capture is out of the question. Even if Mercury did have a small satellite, the Sun's pull would disturb the orbit of the satellite, causing it to fall into the planet.
While Venus has a greater gravitational pull, it still faces the same problem. It's simply too close to the sun to hold on to another body. However, in the past, Venus might have had a moon that spiraled into the planet after collision with another body that might or might not have caused the planet to flip along its axis.
Most likely because they are too close to the Sun. Any moon with too great a distance from these planets would be in an unstable orbit and be captured by the Sun. If they were too close to these planets they would be destroyed by tidal gravitational forces. The zones where moons around these planets could be stable over billions of years is probably so narrow that no body was ever captured into orbit, or created in situ when the planets were first being accreted.
Moons or natural satellites are either created during the creation of the planet/solar system, or are captured.
Mercury doesn't have a gravitational pull powerful enough to hold anything else in orbit around itself. That's why it doesn't even have an atmosphere. And proximity to the Sun ensures that any object coming within Mercury's vicinity is sucked into the Sun directly. So capture is out of the question. Even if Mercury did have a small satellite, the Sun's pull would disturb the orbit of the satellite, causing it to fall into the planet.
While Venus has a greater gravitational pull, it still faces the same problem. It's simply too close to the sun to hold on to another body. However, in the past, Venus might have had a moon that spiraled into the planet after collision with another body that might or might not have caused the planet to flip along its axis.
