DESTINY+: Japan's mission to visit active asteroid Phaethon

Artist's concept of DESTINY+. Credit: JAXA

• Launch Date: NET 2025
• Launch Site: Uchinoura Space Center, Japan
• Launch Vehicle: Epsilon S
• Mission Type: Demonstration & Flyby
• Target: Phaethon
• Dimensions: N/A
• Mass: 480 Kilograms Including Fuel

The Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science (DESTINY PLUS, or +) spacecraft is part of a technology demonstration by Japan. The mission will allow smaller rockets to launch smaller spacecraft to more distant targets.

The Mission

The DESTINY spacecraft proposal has been around since the early 2010s. Later on, the possibility of flying by the unusual active asteroid Phaethon presented itself, and the "+" was added. The mission is planned to launch on a small Epsilon rocket from the Uchinoura Space Center in Japan in 2025.

DESTINY+ Mission Profile. Credit: JAXA

After launch, the spacecraft will spend one-and-a-half years raising its orbit with its ion engines. Once the orbit is sufficiently raised, DESTINY+ will make a flyby of the Moon to put it into heliocentric orbit, similar to the method used by ICE.

The spacecraft will spend a few years testing out its novel technologies, and sampling interplanetary dust. In 2029 or 2030, if the spacecraft launches on schedule, it will make a flyby of active asteroid Phaethon. The flyby will be quite quick, with a relative velocity of 33 kilometres per second.

DESTINY+ Phaethon flyby. Credit: JAXA

The Target

Phaethon is unusual, because though it is not a comet, it has a tail of debris. This was originally believed to have been caused by dust released because of solar heating. However, new observations in 2021 seem to indicate that the tail primarily consists of Sodium ions. This is quite similar to the exosphere of Mercury, which will be analyzed by JAXA's Mio spacecraft aboard BepiColombo when it arrives at Mercury.

Artist's illustration of dust and sodium being emmitted by Phaethon. Credit: NASA/JPL-Caltech/IPAC/Tim Pyle

Like a comet, Pheathon only possesses a tail when it's close to the Sun. Phaethon's orbit is quite elliptical, taking it all the way past Mars at its farthest point, and closer to the Sun than Mercury at its lowest point. While most meteor showers are caused by Earth moving into the path of comets, the Gemini meteors of December are actually caused by debris from Phaethon.

Animation of Phaethon radio images from the late Arecibo Observatory. Credit: Arecibo Observatory/NASA/National Science Foundation

• Date Discovered: October 11, 1983
• Designation: 3200 Phaethon (1983 TB)
• Class: Apollo [NEO]
• Radius: 3.13 Kilometres
• Rotational Period: 3.6 Hours
• Orbital Period: 523.51 Days (1.43 Years)