It is impossible for any spacecraft to land on the Sun, a reality governed by the extreme physical, thermal, and mechanical forces of our star. The question of a landing is dismissed by three major barriers: the Sun’s fundamental state of matter, the overwhelming heat load, and the immense energy required to slow a probe down enough to fall toward it. Exploring the Sun requires overcoming engineering challenges far more demanding than traveling to any rocky planet. Solar missions instead focus on brief, high-speed passes through the star’s upper atmosphere.
Why the Sun Has No Surface
The concept of “landing” requires a solid surface, which the Sun does not possess. Our star is not a rocky body like Earth or Mars; it is a gigantic, super-hot sphere composed almost entirely of gas and plasma. Plasma is a distinct state of matter, often described as an ionized gas, where electrons have been stripped from their atoms due to extreme temperature.
The Sun is fluid throughout its structure, from the core to the outermost atmosphere. As you move inward from space, the density increases gradually, never resulting in a fixed, solid ground. The increasing pressure compresses the plasma, but it remains a fluid, preventing any object from standing on it.
What we perceive as the Sun’s visible edge is a layer called the photosphere. This layer is not a solid boundary but merely the point where the gas becomes dense enough to be opaque. The photosphere is about 250 miles thick, with temperatures around 10,000 degrees Fahrenheit, but it offers no physical structure to support a landing.
The Problem of Extreme Temperature
The temperature barrier is a formidable challenge, particularly because the Sun’s outer atmosphere is counterintuitively hotter than its visible surface. The photosphere temperature is approximately 10,000 degrees Fahrenheit (5,500 degrees Celsius). Moving outward, the temperature drops initially, but then spikes dramatically in the corona, the Sun’s tenuous outer atmosphere.
The corona can reach temperatures between 1.8 million and 3.6 million degrees Fahrenheit (1 to 2 million degrees Celsius). While the density of the corona is extremely low, the intense thermal radiation presents a substantial problem for any approaching material. No known man-made material could maintain structural integrity when exposed to the full radiation load of the Sun at close range.
Even with the most advanced heat shields, the constant barrage of radiation would rapidly break down materials. Heat shields are designed to reflect the intense solar energy, but a prolonged approach would lead to inevitable failure. This high thermal load remains a constant limitation, forcing spacecraft to rely on sophisticated cooling systems and rapid flybys to survive.
The Challenge of Approach Velocity
The difficulty of reaching the Sun is not just about heat, but also about orbital mechanics and velocity. Earth, and everything launched from it, is already traveling at an immense speed of approximately 67,000 miles per hour as it orbits the Sun. This velocity is almost entirely sideways relative to the Sun, and it is what keeps Earth from falling directly into the star.
A spacecraft attempting to fall into the Sun must first cancel out this tremendous sideways momentum. To completely nullify Earth’s orbital velocity, a probe would need to fire its engines backward, which requires an extraordinary amount of propellant. It takes 55 times more energy to send a spacecraft toward the Sun than it does to send one to Mars.
Since current rocket technology cannot carry enough fuel for this massive deceleration, engineers must employ clever maneuvers. Missions use planetary gravity assists, specifically from Venus, to act as a cosmic brake. Each pass by Venus saps a small amount of the spacecraft’s orbital energy, incrementally shrinking its path closer to the Sun.
Missions That Touch the Sun
Despite the impossibility of a landing, humanity has successfully sent missions to study the Sun up close. The Parker Solar Probe is the foremost example, designed to pass through the Sun’s outer atmosphere, the corona. This spacecraft is the fastest human-made object, moving at speeds up to 430,000 miles per hour during its closest approaches.
The probe survives by using a specialized, 4.5-inch-thick carbon-composite heat shield, which keeps the interior instruments at room temperature. The craft’s rapid movement is also a factor, as it spends minimal time within the most intense thermal zones. The shield is designed to endure temperatures of up to 2,500 degrees Fahrenheit on its sun-facing side.
Scientists define “touching” the Sun as crossing the Alfvén critical surface. This boundary, located about 8 million miles from the visible surface, is where the Sun’s magnetic field begins to control the solar wind material. The Parker Solar Probe crossed this boundary in 2021, meaning it was briefly immersed in the plasma magnetically connected to the Sun, providing the first direct measurements of the star’s atmosphere.