A grain of sand weighs about 1 milligram (a thousandth of a gram).
Venus is the closest planet to Earth, but it does not have oceans or human life like Earth. Depending on their relative positions in their orbits, Mercury, Earth, and Mars each swap that title between them. For example, when on opposite sides of their orbits, Venus and Earth can be more than 150 million miles apart, while Mars and Mercury can be as close as 74 and 31 million miles from Venus, respectively. It's a result of the circular nature of their orbits. The closest planet to Venus either earth or mercury depending where the planets are in their orbits.
Venus has a very strong greenhouse effect. A greenhouse effect is when the gases in the atmosphere trap more of the Sun's heat. A lot of carbon dioxide, a very dense atmosphere, and a thick blanket of clouds help trap the sun's heat. The transfer of heat by atmospheric currents means both the night and day sides are almost the same temperature.
Venus is like this because it is closer to the Sun than Earth so it is naturally hotter. On Earth, it is cool enough for water to condense and form oceans, where carbon dioxide can be absorbed. On Venus, water cannot condense in order to absorb the carbon dioxide so all of it stays in the atmosphere.
The temperature is about 460 °C.
AntimatterAntimatter could be considered the opposite of "normal" matter. We know that the matter that is all around us and makes us up is built of atoms, and these atoms are made up of protons, neutrons and electrons. In antimatter, atoms would be constructed of anti-protons, anti-neutrons and anti-electrons (which we know as positrons). As electrons orbit a nucleus of protons and neutrons in the "regular" matter we know, positrons would orbit a nucleus of anti-protons and anti-neutrons to make up antimatter atoms.
We currently use anti-electrons (positrons) on a regular basis in the medical application we know as PET imaging. Additionally, we use anti-protons in nuclear research. The Large Hadron Collider runs with protons and antiprotons circulating in the acceleration ring (in opposite directions), and then "collided" in an experimental area packed with sensors and detectors.
It should be noted that matter and antimatter don't "like" each other. Any "contact" between the two leads to mutual annihilation. In the case of the positron, which is produced in beta plus decay, that positron will eventually "run into" an electron, and mass of the two particles will be entirely converted into energy. Links have been included for further investigation, and you'll find them below.
The answer is not a simple one, because it depends on the criteria used.
As you move upward from the surface, gravity and the density of air gradually decrease until you reach a near-vacuum. Listed below are some valid interpretations of the boundary between Earth and space.
For starters, astronauts can say they've been to space after passing only the 50-mile mark (80 kilometers, 264,000 feet). NASA awards its astronaut wings to any individual reaching that altitude.
Meanwhile the boundary recognized by many in the space industry is the Karman line at a somewhat arbitrary 62.137 miles (100 kilometers). Scientist Theodore von Kármán long ago calculated that at this altitude the atmosphere is so thin that it's negligible, and conventional aircraft can no longer function because they can't go fast enough to get any kind of aerodynamic lift. This 62-mile (100 km) boundary is accepted by the Federation Aeronautique Internationale (FAI), which sets aeronautical standards.
Recently, with data from a new instrument developed by scientists at the University of Calgary, scientists defined that space begins 73 miles (118 kilometers) above Earth's surface. NASA's mission control uses 76 miles (122 kilometers) as their re-entry altitude because below that the shuttle switches from steering with thrusters to maneuvering with aerodynamic surfaces. Others point out that the "Now Entering Space" sign should be posted way out at 13 million miles (21 million kilometers) because that's the boundary where Earth's gravity is no longer dominant.
Meteorologists will tell you the atmosphere ends 600 miles (1000 kilometers) up, but even at half that distance air molecules are few and far between. Meteors start to burn about 40 miles (65 kilometers) up due to atmospheric friction. The drop in atmospheric density is obvious even lower. Most humans need supplemental oxygen above a mere 10,000 feet (3 kilometers) and the highest habitations have been near 16,000 feet (5 kilometers).