Japan launches $578 million MMX mission to return samples from Phobos

MMX lifted off from the Tanegashima Space Center in southern Japan at 4:41 a.m. local time on 20 October [1][4][9]. That was 3:41 p.m. EDT on 19 October [1][9].

If it works, laboratories on Earth will hold the first physical samples from the Martian system, material that could settle a decades-old argument about how Phobos and Deimos formed [4][9][13]. The launch also put Japan's H3 rocket on its first interplanetary flight and committed five space agencies to a five-year round trip [7][8][11]. Until then, the origin question stays open. Separation came about 71 minutes after liftoff, and JAXA project manager Yasuhiro Kawakatsu said the spacecraft had unfurled its solar panels and was in a "very stable condition" [1][9]. The mission cost $578 million [9][13]. Arrival at Mars is scheduled for August 2027, after about 10 months in transit [1][8][13].

The question Phobos can answer

Scientists have argued for decades over whether Phobos and Deimos are captured asteroids or rubble thrown into orbit by a huge impact on Mars [4][6][8]. Remote instruments have not settled it [7]. A sample in a laboratory might [7][8].

The target is at least 10 grams of material [4][11][12][13]. MMX will collect it over two separate touchdowns on Phobos [1][4][12]. Phobos is an easier target than Mars itself, because its weak gravity lets a spacecraft land and leave without heavy propulsion [12][13]. Its size depends on who is measuring: about 22 km wide [1], around 25 km across [6], or 27 by 22 by 18 km [11][13]. Phobos orbits about 6,000 km above Mars [11][13]. It circles the planet three times a day [11][14].

Spacecraft, rover and route

MMX has three modules: a propulsion module, an exploration module with landing legs and sampling gear, and a return module for the trip home [7][8][12][14]. It weighs about 4,480 kilograms at launch [12]. It is roughly 9 metres long [7]. The rocket flew in the H3-24L configuration, with two LE-9 main engines, four solid boosters and an extended payload fairing [12]. It was the 10th H3 liftoff [1]. At Mars, MMX will fly a quasi-satellite orbit, circling Mars in step with Phobos so it appears to loop around the moon [1][7][8].

The 25-kilogram IDEFIX rover, built by France's CNES and Germany's DLR, is due to deploy in late 2028 or early 2029 [1][3][7]. On Phobos it would weigh about 15 grams [7][14].

MMX carries 13 science instruments: cameras, a lidar, spectrometers [6][8]. Sampling uses bursts of pressurised gas to lift surface dust, plus a corer that bites about 2 cm deep [6][14].

Why Japan is trying it

Hayabusa2 brought Ryugu material back in December 2020 [3][6]. Russia's Phobos-Grunt launched in 2011 but never fired the engines that would have sent it to Mars [6][8]. The H3 rocket failed on its inaugural flight in 2023 and again in December 2025, its second failure in seven flights, later traced to a payload fairing separation problem [3][11]. MMX is the H3's first interplanetary mission [11]. The Mars window opens every 26 months, and JAXA had backups from 21 October to 9 November [3][12].

What happens next

MMX should spend about three years in the Martian system [1][4]. The main spacecraft is expected to land and collect samples around 2029, leave in 2030 and drop its capsule in Australia in 2031 [3][4][6][13].

The origin question stays open until that capsule is opened.