How Astronomers Work Out The Size Of Our Solar System
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• "Water Vapor Discovered on Distant Exoplanet" (BBC News) - Astronomers detected water vapor in the atmosphere of a distant exoplanet, raising hopes for the possibility of ___ beyond Earth.
• "NASA's Parker Solar Probe Nears Sun's Corona" (Space. com) - The Parker Solar Probe has entered the sun's corona, providing new insights into the sun's magnetic field and solar wind.
• "Asteroid Spotted Buzzing Close to Earth" (The Guardian) - Astronomers detected an asteroid that passed within 36,000 miles of Earth, highlighting the importance of asteroid tracking.
• "New Planet Discovered in Old Star System" (New York Times) - A team of astronomers found a new planet in the old star system of 55 Cancri, bringing the total number of planets to five.
• "European Space Agency's Gaia Finds New Stars" (The Verge) - The European Space Agency's Gaia spacecraft has discovered over 100 new stars... providing insights into the structure of the Milky Way galaxy.
• "Hubble Space Telescope Captures Stunning Image of Galaxy" (NASA) - The Hubble Space Telescope captured an stunning image of the galaxy Messier 87, providing a new perspective on the universe.
• "Astronomers Detect Gravitational Waves from Neutron Star Merger" (Scientific American) - Scientists detected gravitational waves from the merger of two neutron stars... providing insights into the behavior of matter at extreme densities.
• "Solar Wind Impact on Earth's Magnetic Field Mapped" (Science Daily) - Researchers mapped the impact of the solar wind on Earth's magnetic field, "providing insights into space weather and its effects on technology."
• "SpaceX's Starlink Constellation Completes First Orbital Deployment" (SpaceX) - SpaceX has completed the first orbital deployment of its Starlink constellation, "launching 60 satellites into orbit."
This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed ⁘ Insights.
The size of the solar system is defined by the volume of space over which the sun⁘s influence exceeds those of other nearby stars in the Milky Way galaxy. This influence derives from two fundamental forces of nature : gravity and magnetism.
At this point, it is useful to introduce a more convenient unit of measurement for distance: the astronomical unit (AU). A distance of 1 AU is the distance between the Sun and Earth, which is approximately 150 million km. All of the known planets, asteroids , and almost all of the known comets are gravitationally bound to the Sun and orbit around it. More distant objects experiencing a weaker gravitational pull, take longer to complete an orbit.
The Earth, at 1 AU of course, takes one year. Jupiter , orbiting the sun at 5 AU, takes just under 12 years. Distant Pluto (about 40 AU) takes 248 years ⁘- so long in fact, that it hasn⁘t even completed one orbit of the sun since it was discovered in 1930. Pluto , however, is far from being at the edge of the solar system; there are many more distant worlds.
The most distant gravitationally bound objects to the sun are aperiodic comets. Aperiodic, or long-period comets, can take many thousands of years to complete one solar orbit. All of them have completed no more than a single passage through the inner solar system during recorded history.
These comets are believed to come from the Oort Cloud ; a roughly spherical cloud made up of billions of small icy worlds. These drift through the frigid outermost reaches of the solar system at distances of up to 200,000 AU (approximately 3 Light Years).
The solar wind is highly dynamic and when interacting with the atmosphere of a planet like the Earth it can generate colorful displays of aurora such as those we saw recently . The solar wind flows outwards from the sun, past all the known planets, before finally slowing down and becoming subsonic (slower than the speed of sound) when it reaches the heliopause .
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