Why can't I make a unique pointer to an array, when I can make a shared pointer?

The following is invalid:

#include <memory>
#include <iostream>
typedef double zip[10];

int main()
{
    std::unique_ptr<zip> s = std::make_unique<zip>();
    (*s)[0] = 2.0;
    std::cout << (*s)[0] << std::endl;
    return 0;
}

But the following is perfectly valid:

int main()
{
    std::shared_ptr<zip> s = std::make_shared<zip>();
    (*s)[0] = 2.0;
    std::cout << (*s)[0] << std::endl;
    return 0;
}

Why the discrepancy? What am I missing?