Message: #2  2022-07-15  

The Sun, Moon, and brightest planets were visible to the naked eyes of
ancient astronomers, and their observations and calculations of the
movements of these bodies gave rise to the science of astronomy. Today
the amount of information on the motions, properties, and compositions
of the planets and smaller bodies has grown to immense proportions,
and the range of observational instruments has extended far beyond the
solar system to other galaxies and the edge of the known universe. Yet
the solar system and its immediate outer boundary still represent the
limit of our physical reach, and they remain the core of our
theoretical understanding of the cosmos as well. Earth-launched space
probes and landers have gathered data on planets, moons, asteroids,
and other bodies, and this data has been added to the measurements
collected with telescopes and other instruments from below and above
Earth’s atmosphere and to the information extracted from meteorites
and from Moon rocks returned by astronauts. All this information is
scrutinized in attempts to understand in detail the origin and
evolution of the solar system—a goal toward which astronomers
continue to make great strides.

Message: #1  2022-07-15  

Located at the centre of the solar system and influencing the motion
of all the other bodies through its gravitational force is the Sun,
which in itself contains more than 99 percent of the mass of the
system. The planets, in order of their distance outward from the Sun,
are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Four planets—Jupiter through Neptune—have ring systems, and all
but Mercury and Venus have one or more moons. Pluto had been
officially listed among the planets since it was discovered in 1930
orbiting beyond Neptune, but in 1992 an icy object was discovered
still farther from the Sun than Pluto. Many other such discoveries
followed, including an object named Eris that appears to be at least
as large as Pluto. It became apparent that Pluto was simply one of the
larger members of this new group of objects, collectively known as the
Kuiper belt. Accordingly, in August 2006 the International
Astronomical Union (IAU), the organization charged by the scientific
community with classifying astronomical objects, voted to revoke
Pluto’s planetary status and place it under a new classification
called dwarf planet. For a discussion of that action and of the
definition of planet approved by the IAU, see planet.