Exploring Mars: Its Closest Approach to Earth Until 2035
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Chapter 1: The Martian Perspective
Mars, characterized by a diminished polar ice cap and a significant angular size, is illustrated here during its summer season while Earth approaches opposition. This event occurs when the Sun, Earth, and Mars align in a straight line. The image, captured on September 25, 2020, was taken just 11 days prior to the closest approach of the red planet. A 14" amateur telescope was utilized for this observation. Notably, despite its apparent size, Mars remains considerably smaller than the Moon.
On October 6, 2020, Mars reaches its closest position to Earth until 2035.
Earth's orbit around the Sun is nearly circular, completing a full revolution in 365 days. In contrast, Mars follows a more elliptical, slower orbit, taking 687 days for a single revolution. Consequently, Earth encounters its "closest approach" to Mars approximately every 780 days, which is a little over two Earth years.
The planets orbit the Sun in the same direction but at varying speeds and distances.
Section 1.1: The Dance of Orbits
The relative orbits of Earth and Mars illustrate that Earth overtakes Mars about every 780 days. However, Mars appears largest when this close encounter aligns with its perihelion, or closest approach to the Sun.
NASA's Mars 2020 mission, featuring the Perseverance rover, was launched in July 2020 and is set to arrive at Mars in February 2021. The current close approach of Earth to Mars provides an ideal launch window that occurs only every few years.
These optimal close approaches significantly reduce the fuel needed for missions to Mars.
As Mars travels in its orbit, its angular size can vary dramatically, ranging from approximately 3 arc-seconds at its smallest to around 25 arc-seconds at its largest. When Mars is at its peak brightness, it can appear larger than Saturn and nearly as large as Jupiter from Earth.
From Earth, Mars's angular size fluctuates more than any other planet.
Section 1.2: Observational Opportunities
Watch Mars as it makes its closest approach to Earth until 2035.
The variability in Mars's size is significant; it can change by a factor of 8 from its smallest to largest angular diameters.
This composite of images from September 2020 illustrates Mars's rotation over an hour, highlighting the shifting polar cap at its south pole. Unlike Earth, the seasons on Mars are influenced primarily by its elliptical orbit rather than its axial tilt.
The orbits of the inner solar system planets, while nearly circular, exhibit some ellipticity. When Mars is closest to the Sun, it comes within 0.38 AU of Earth's orbit, but at its farthest point, it stretches to 0.66 AU away.
Martian winters occur when it is farthest from the Sun, with summers coinciding when it is closest.
Chapter 2: Viewing Mars's Changes
Explore the closest approach of Mars in 15 years.
The images from the Hubble Space Telescope, taken in 1997, illustrate the changing Martian surface in terms of ice and cloud cover, reflecting the seasons on Mars and its distance from Earth. For example, the September image shows a warmer Martian landscape compared to the July snapshot.
When Mars's summer aligns with Earth's closest approach, the planet appears at its largest.
Dust storms are prevalent during Martian summer, as evidenced by the comprehensive storm that enveloped the planet in 2001. Such storms can obscure surface features significantly and occur most frequently during warmer periods.
This year, Earth passes Mars when it is near its perihelion, resulting in the closest approach until 2035.
The distances between Earth and Mars during these closest encounters range from about 0.38 AU to just under 0.7 AU, influenced by the elliptical nature of Mars's orbit.
Currently, favorable weather conditions enable even amateur astronomers to observe surface features, including the shrinking polar ice cap.
Mars remains a prominent celestial object throughout October, making it an excellent time for skywatching.
Every 780 days, the alignment of the Sun, Earth, and Mars occurs, with Earth approaching Mars closely within days of this event. When this alignment coincides with Mars's perihelion, the view from Earth is particularly striking.
At its maximum size of 25.1 arc-seconds, Mars appears point-like to the naked eye without magnification.
On October 2, 2020, the nearly full Moon approached Mars in the sky, illustrating the significant size difference between the two celestial bodies, with the Moon appearing around 75 times larger than Mars in angular size.
In summary, this year’s astronomical events present a fantastic opportunity for enthusiasts to observe Mars as it approaches Earth, culminating in a spectacular view of the red planet.
Starts With A Bang is crafted by Ethan Siegel, Ph.D., author of Beyond The Galaxy and Treknology: The Science of Star Trek from Tricorders to Warp Drive.